Inter-component prediction

ABSTRACT

Reconstructing a second component signal relating to a second component of a multi-component picture from a spatially corresponding portion of a reconstructed first component signal and a correction signal derived from a data stream for the second component promises increased coding efficiency over a broader range of multi-component picture content. By including the spatially corresponding portion of the reconstructed first component signal into the reconstruction of the second component signal, any remaining inter-component redundancies/correlations present such as still present despite a possibly a priori performed component space transformation, or present because of having been introduced by such a priori performed component space transformation, for example, may readily be removed by way of the inter-component redundancy/correlation reduction of the second component signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of copending InternationalApplication No. PCT/EP2014/057090, filed Apr. 8, 2014, which isincorporated herein by reference in its entirety, and additionallyclaims priority from US Applications Nos. 61/809,608, filed Apr. 8,2013, 61/846,450, filed Jul. 15, 2013, and EP 14 150 373.0, filed Jan.7, 2014, all of which are incorporated herein by reference in theirentirety.

BACKGROUND OF THE INVENTION

The present application is concerned with inter-component prediction inmulti-component picture coding such as between luma and chroma.

In image and video signal processing, color information is mainlyrepresented in a color space typically consisting of three componentslike R′G′B′ or Y′CbCr. The first component, Y′ in the case of Y′CbCr, isoften referred to as the luma and the remaining two components, the Cband the Cr components or planes in the case of Y′CbCr, are referred toas the chroma. The advantage of the Y′CbCr color space over the R′G′B′color space is mainly the residual characteristic of the chromacomponents, i.e., the chroma components contain less energy or amplitudecomparing to the chroma signals of absolute color spaces like R′G′B′. Inparticular for Y′CbCr, the luma component implies the grey scaleinformation of the image or video and the chroma component Cb impliesthe difference relative to the blue primary, respectively Cr denotes thedifference relative to the red primary.

In the application space of image and video compression and processing,Y′CbCr signals are advantageous as compared to R′G′B′ due to the factthat the color space transformation from R′G′B′ to Y′CbCr reduces orremoves the correlation between the different color components orplanes. In addition to the correlation removal, less information has tobe transmitted, and hence, the color transformation acts as acompression approach too. Such a pre-processing in correlation removalor reduction enables higher compression efficiency while maintaining orincreasing the complexity in a meaningful amount as an example. A hybridvideo compression scheme is often designed for Y′CbCr input because thecorrelation between the different color components is removed or reducedand the designs of hybrid compression schemes only have to consider theseparate processing of the different components. However, thetransformation from R′G′B′ to Y′CbCr and vice versa is not lossless, andhence, information, i.e., sample values available in the original colorspace might be lost after such a color transformation. This issue can beavoided by using color spaces involving a lossless transformation fromthe original color space and back to the original color space, e.g., theY′CoCg color space when having R′G′B′ input. Nevertheless, fixed colorspace transformations might lead to sub-optimal results depending on theapplication. For image and video compression, fixed colortransformations are often sub-optimal for higher bit rates andnon-natural signals with high or without correlation between the colorplanes. In the second case, a fixed transformation would introducecorrelation between the different signals, and in the first case, thefixed transformation might not remove all the correlation between thedifferent signals. Furthermore, due to the global application of thetransformation, correlation might not be completely removed from thedifferent components or planes locally or even globally. Another issueintroduced by a color space transformation lies in the architecture ofan image or video encoder. Usually, the optimization process tries toreduce a cost function, which is often a distance metric defined overthe input color space. In the case of transformed input signals, it canbe difficult to achieve an optimal result for the original input signaldue to additional processing steps. Consequently, the optimizationprocess might result in a minimum cost for the transformed signal butnot for the original input signal. Although the transformations areoften linear, the cost calculation in the optimization process ofteninvolves a signalling overhead and the cost for the final decision isthen calculated by a Lagrangian formula. The latter might lead todifferent cost values and different optimization decision. The colortransformation aspect is especially crucial in the domain of colorrepresentation as modern image and video displays usually use the R′G′B′color composition for content representation. Generally speaking,transformations are applied when correlation within the signal orbetween the signals should be removed or reduced. As a consequence, thecolor space transformation is a special case of the more generictransformation approach.

Accordingly, it would be favorable to have a multi-component picturecoding concept at hand which is even more efficient, i.e. achieveshigher bitrates over a broader range of multi-component picture content.

SUMMARY

One embodiment has a decoder configured to decode a multi-componentpicture spatially sampling a scene with respect to different components,by reconstructing a first component signal relating to a first componentof the multi-component picture from a data stream; reconstructing aportion of a second component signal relating to a second component ofthe multi-component picture from a spatially corresponding portion ofthe reconstructed first component signal and a correction signal derivedfrom the data stream, wherein the first and second components are colourcomponents and the first component signal is a prediction residual of atemporally, spatially or inter-view prediction of the first component ofthe multi-component picture and the second component signal is aprediction residual of a temporal, spatial or inter-view prediction ofthe second component of the multi-component picture.

Another embodiment has an encoder configured to encode a multi-componentpicture spatially sampling a scene with respect to different components,by encoding a portion of a second component signal relating to a secondcomponent of the multi-component picture by prediction from a spatiallycorresponding portion of a reconstructed first component signal andinserting a correction signal for correcting the prediction into thedata stream.

According to another embodiment, a method for decoding a multi-componentpicture spatially sampling a scene with respect to different componentsmay have the steps of: reconstructing a first component signal relatingto a first component of the multi-component picture from a data stream;and reconstructing a portion of a second component signal relating to asecond component of the multi-component picture from a spatiallycorresponding portion of the reconstructed first component signal and acorrection signal derived from the data stream, wherein the first andsecond components are colour components and the first component signalis a prediction residual of a temporally, spatially or inter-viewprediction of the first component of the multi-component picture and thesecond component signal is a prediction residual of a temporal, spatialor inter-view prediction of the second component of the multi-componentpicture.

According to another embodiment, a method for encoding a multi-componentpicture spatially sampling a scene with respect to different componentsmay have the steps of: encoding a portion of a second component signalrelating to a second component of the multi-component picture byinter-component prediction on the basis of a spatially correspondingportion of a reconstructed first component signal and inserting acorrection signal for correcting the inter-component prediction into thedata stream, wherein the first and second components are colourcomponents and the first component signal is a prediction residual of atemporally, spatially or inter-view prediction of the first component ofthe multi-component picture and the second component signal is aprediction residual of a temporal, spatial or inter-view prediction ofthe second component of the multi-component picture.

The present invention is based on the finding that reconstructing asecond component signal relating to a second component of amulti-component picture from a spatially corresponding portion of areconstructed first component signal and a correction signal derivedfrom a data stream for the second component promises increased codingefficiency over a broader range of multi-component picture content. Byincluding the spatially corresponding portion of the reconstructed firstcomponent signal into the reconstruction of the second component signal,any remaining inter-component redundancies/correlations present such asstill present despite a possibly a priori performed component spacetransformation, or present because of having been introduced by such apriori performed component space transformation, for example, mayreadily be removed by way of the inter-component redundancy/correlationreduction of the second component signal.

In accordance with an embodiment of the present application, themulti-component picture codec is construed as a block-based hybrid videocodec operating in units of code blocks, prediction blocks, residualblocks and transform blocks, and the inter-component dependency isswitched on and off at a granularity of the residual blocks and/ortransform blocks by a respective signalling in the data stream. Theadditional overhead for spending the signalling is over-compensated bythe coding efficiency gain as the amount of inter-component redundancymay vary within a picture. In accordance with an embodiment of thepresent application, the first component signal is a prediction residualof a temporally, spatially or inter-view prediction of the firstcomponent of the multi-component picture and the second component signalis a prediction residual of a temporal, spatial or inter-view predictionof the second component of the multi-component picture. By this measure,the inter-component dependency exploited focuses on remaininginter-component redundancies so that the inter-component prediction maytend to show a smoother spatial behavior.

In accordance with an embodiment, a first weight at which the spatiallycorresponding portion of the reconstructed first component signalinfluences the reconstruction of the second component signal, denoted ain the following, is adaptively set a sub-picture granularity. By thismeasure, the intra-picture variation in inter-component redundancy maybe more closely followed. In accordance with an embodiment, a mixture ofa high-level syntax element structure and sub-picture granularityfirst-weight syntax elements is used in order to signal the first weightat the sub-picture granularity, wherein the high-level syntax elementstructure defines a mapping from a domain set of possible bin strings ofa predetermined binarization of the first-weight syntax elements onto aco-domain of possible values of the first weight. By this measure, theoverhead for a side information for controlling the first weight is keptlow. The adaptation may be done forward adaptively. A syntax element maybe used per block such as residual or transform block, which has alimited number of signalable states which symmetrically index one of anumber of weight values for a symmetrically distributed around zero. Inone embodiment, the number number of signalable states is uneven withthe number of weight values including zero, wherein the signalling ofzero is used so as to signal the non-use of inter-component predictionso that an extra flag becomes obsolete. Further, the magnitude issignaled before the conditionally signaled sign, with the magnitude ismapped onto the number of weight values and if the magnitude is zero,the sign is not signaled so that signalization costs are furtherreduced.

In accordance with an embodiment, a second weight at which thecorrection signal influences the reconstruction of the second componentsignal, is set at a sub-picture granularity, either in addition to, oralternatively to, the adaptive setting of the first weight. By thismeasure, the adaptivity of inter-component redundancy reduction mayfurther be increased. In other words, in accordance with an embodiment,in reconstructing the second component signal, weights of a weighted sumof the correction signal and the spatially corresponding portion of thereconstructed first component signal, may be set at a sub-picturegranularity. The weighted sum may be used as a scalar argument of ascalar function which is, at least per picture, constant. The weightsmay be set in a backward-driven manner based on a local neighbourhood.The weights may be corrected in a forward-driven manner.

In accordance with an embodiment, the domain where the reconstruction ofthe second component signal from a spatially corresponding portion ofthe reconstructed first component signal using the correction signal isperformed, is the spatial domain. Alternatively, the spectral domain isused. And even alternatively, the domain used is changed between spatialand spectral domain. The switching is performed at sub-picturegranularity. It turned out that the ability to switch, at sub-picturegranularity, the domain where the combination of the reconstructed firstcomponent signal and the correction signal takes place, increases thecoding efficiency. The performing the switching may be done inbackward-adaptive manner or in a forward-adaptive manner.

In accordance with an embodiment, a syntax element in the data stream isused to enable changing the role of the first and second componentsignals within the components of the multi-component picture. Theadditional overhead for signalling the syntax element is low compared tothe possible gain in coding efficiency.

In accordance with an embodiment, the reconstruction of the secondcomponent signal is allowed to switch, at sub-picture granularity,between the reconstruction based on the reconstructive first componentsignal only, and reconstructing same based on the reconstructed firstcomponent signal and a further reconstructed component signal of afurther component of the multi-component picture. At relatively lowadditional effort, this possibility increases the flexibility inremoving residual redundancies between components of the multi-componentpicture.

Likewise, in accordance with an embodiment, a first syntax element inthe data stream is used in order to, globally or at an increased scopelevel, enable or disable the reconstruction of the second componentsignal based on the reconstructed first component signal. If enabled,sub-picture level syntax elements in the data stream are used to adaptthe reconstruction of the second component signal based on areconstructed first component signal at a sub-picture granularity. Bythis measure, spending side information for the sub-picture level syntaxelements may merely be employed in application cases or multi-componentpicture contents for which the enablement results in a coding efficiencygain.

Alternatively, the switching between enablement and disablement isperformed locally in a backward-driven manner. In this case, the firstsyntax element does not even need to be present in the data stream. Inaccordance with an embodiment, for example, the local switching isperformed locally depending on a check whether first and secondcomponent signals are prediction residuals of a spatial prediction withthe intra-prediction mode of the spatial prediction coinciding, or notdeviating by more than a predetermined amount. By this measure, thelocal switching between enablement and disablement does not consumebitrate.

In accordance with an embodiment, a second syntax element in the datastream is used so as to switch between adaptive reconstruction of thesecond component signal based on the reconstructed first componentsignal at sub-picture granularity forward-adaptively using sub-picturelevel syntax elements in the data stream, and non-adaptively performingthe reconstruction of the second component signal based on thereconstructed first component signal. The signalling overhead for thesecond syntax element is low compared to the possibility of avoiding theoverhead for transmitting the sub-picture level syntax elements formulti-component picture content for which non-adaptively performing thereconstruction is already efficient enough.

In accordance with an embodiment, the concept of inter-componentredundancy reduction is transferred onto a three chroma componentpicture. In accordance with an embodiment, luma and two chromacomponents are used. The luma component may be chosen as the firstcomponent.

In accordance with an embodiment, the sub-picture level syntax elementfor adapting the reconstruction of the second component signal from thereconstructed first component signal is coded within the data streamusing a Golomb-Rice code. The bins of the Golomb-Rice code may besubject to binary arithmetic coding. Different contexts may be used fordifferent bin positions of the Golomb-Rice code.

In accordance with an embodiment, the reconstruction of the secondcomponent signal from the reconstructed first component signal involvesa spatial re-scaling and/or a bit depth precision mapping on thespatially corresponding portion of the reconstructed first componentsignal. The adaptation of the spatially rescaling and/or performance ofthe bit depth precision mapping, may be done in a backward and/orforward adaptive manner. The adaptation of the spatial re-scaling mayinvolve the selection of a spatial filter. The adaptation of theperformance of the bit depth precision mapping may involve the selectionof a mapping function.

In accordance with an embodiment, the reconstruction of the secondcomponent signal from the reconstructed first component signal is doneindirectly via a spatially low-pass filtered version of thereconstructed first component signal.

Advantageous implementations of embodiments of the present applicationare the subject of the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will be detailed subsequentlyreferring to the appended drawings, in which:

FIG. 1 shows a block diagram of an encoder configured to encode amulti-component picture in accordance with an embodiment;

FIG. 2 shows a block diagram of a decoder fitting to the encoder of FIG.1 in accordance with an embodiment;

FIG. 3 schematically shows a picture and its subdivision/partitioninginto various blocks of different type in accordance with an embodiment;

FIG. 4 schematically shows a reconstruction module in accordance with anembodiment of the present application and being built into encoders anddecoders of FIGS. 1 and 2;

FIG. 5 schematically shows a picture with two components, a currentlyinter-component predicted block as well as the spatially correspondingportion within the first (base) component;

FIG. 6 schematically shows a picture with three components so as toillustrate an embodiment where one component constantly serves as thebase (first) component in accordance with an embodiment;

FIG. 7 shows schematically a picture with three components where each ofthe components may serve, alternately, as the first (base) component inaccordance with an embodiment;

FIG. 8 schematically shows a possibility according to which the domainfor inter-component prediction is adaptively changed;

FIG. 9 a schematically shows a possibility of signalling aninter-component prediction parameter;

FIG. 9 b shows the embodiment of FIG. 9 a in more detail;

FIG. 9 c schematically shows the application of the inter-componentprediction parameter which FIGS. 9 a and 9 b relate to for illustrationpurposes; and

FIG. 10 schematically shows a forward adaptive inter-componentprediction in accordance with an embodiment.

DETAILED DESCRIPTION OF THE INVENTION

The description brought forward below starts with the description of adetailed embodiment of an encoder and a description of a detailedembodiment of a decoder fitting to the encoder, wherein aftergeneralized embodiments are presented.

FIG. 1 shows an encoder 100 configured to encode a multi-componentpicture 102 into a data stream 104. FIG. 1 illustrates exemplarily thecase of the multi-component picture 102 comprising three components 106,108 and 110, but the description brought forward below will reveal thatadvantageous embodiments of the present application may be easilyderived from the description of FIG. 1 by transferring the presentthree-component picture example onto an example where merely twocomponents, such as components 106 and 108, are present. Accordinglysome of the elements of encoder 100 shown in FIG. 1 are shown usingdashed lines and are insofar optional features with respect to moregeneralized embodiments as set out further below.

In principle, the encoder of FIG. 1 and all of the embodiments describedhereinafter could operate with any type of “component”. In effect, themulti-component picture 102 is a picture of a scene which samples thescene with respect to the various components 106, 108 and 110 spatiallyat otherwise coinciding conditions with respect to, for example, timestamp, view conditions and the like. In order to ease the understandingof the embodiments further described below, however, it is assumed thatthe components 106, 108 and 110 all relate to the texture and are, forexample, color components such as luma and chroma components, or colorcomponents of any other color space.

The encoder of FIG. 1 is substantially configured to apply block-basedhybrid video coding to each of components 106, 108 and 110 of picture102 separately with, however, using inter-component prediction so as toreduce inter-component redundancies. Inter-component prediction relatesto various aspects as will be outlined in more detail below.

Accordingly, the encoder 100 comprises, per component 106, 108 and 110,a sequence of a prediction residual former 112, here exemplarilyembodied as a subtractor, a transformer 114 and a quantizer 116 seriallyconnected, in the order of their mentioning between an input at which arespective component 106, 108 and 110, respectively arrives, and arespective input of a data stream former 118 configured to multiplex thequantized coefficients and other coding parameters mentioned in moredetail below, into the data stream 104. While a non-inverting input ofprediction residual former 112 is arranged so as to receive therespective component of picture 102, the inverting (subtrahend) inputthereof receives a prediction signal 120 from a predictor 122, the inputof which is connected to the output of quantizer 116 via areconstruction path comprising a sequence of a dequantizer 124, are-transformer 126 and a prediction/residual combiner 128, hereexemplarily embodied as an adder. While the output ofprediction/residual recombiner 126 is connected to an input ofprediction 122, and a first input is connected to an output ofre-transformer 126, a further input thereof receives the predictionsignal 120 output by predictor 122.

Elements 112, 114, 116, 124, 126, 128, 122 and 120 are present withinencoder 100 in a parallel manner for each of components 106 to 110 so asto form three separate block-based hybrid video coding paths 130 ₁, 130₂ and 130 ₃. The indices 1, 2 and 3 are used to distinguish between thedifferent components of picture 102 with index 1 associated withcomponent 106, index 2 associated with component 108 and index 3associated with component 110.

In the example shown in FIG. 1, component 106 represents a kind of “basecomponent” as will become clearer from the description brought forwardbelow. It should be noted, however, and will be discussed also in moredetail below, that the role among components 106 to 110 may be equalizedin that a configuration illustrated and shown in FIG. 1 has been chosenmerely for the sake of an easier understanding of the principles of theembodiments of the present application described in more detail below.In any case, in order to distinguish the elements 112, 114, 116, 124,126, 128, 122 and 120 of paths 130 ₁ to 130 ₃ described so far, theindices are also used with respect to these elements.

As became clear from the note presented above, in the example of FIG. 1components 108 and 110 represent “dependent components” and for thisreason, further elements in addition to those already discussed forcoding paths 130 ₁ to 130 ₃ are connected between these alreadydiscussed elements. In particular, a spatial domain inter-componentprediction residual former 132 is connected, by means of itsnon-inverting input and its output, between prediction residual former112 on the one hand and the input of transformer 114 on the other hand,and likewise, a spatial-domain inter-component prediction and residualrecombiner 134 is connected between retransformer 126 on the one handand prediction/residual recombiner 128 on the other hand. FIG. 1 alsoshows a spectral domain inter-component prediction residual former 136as being positioned, by way of its non-inverting input and its output,between transformer 114 and quantizer 116 with a corresponding spectraldomain inter-component prediction/residual recombiner 138 beingconnected between dequantizer 124 on the one hand and retransformer 126on the other hand. The pair of spatial-domain inter-component predictionformer 132 and corresponding recombiner 134 is fed, at its furtherinput, by a respective spatial domain inter-component residual predictor140, and likewise, the further input of spectral domain inter-viewprediction former 136 along with its associated recombiner 138 is fedwith a spectral domain residual prediction signal 142 provided by aspectral domain inter-component residual predictor 144. At its inputinterface, predictors 140 and 144 are connected with internal nodes ofany of the respective preceding coding paths. For example, predictor 140₂ is connected to the output of prediction residual former 112 ₁, andpredictor 144 ₂ has an input connected to the output of dequantizer 124₁. Likewise, predictors 140 ₃ and 144 ₃ have an input connected to theoutput of prediction residual former 112 ₂ and dequantizer 124 ₂,respectively, but additionally a further input of predictor 140 ₃ isshown as being connected to the output of prediction residual former 112₁ and a further input of predictor 144 ₃ is shown as being connected tothe output of dequantizer 124 ₁. Predictors 140 and 144 are shown asoptionally generating prediction parameters for implementing a forwardadaptive control of the inter-component prediction performed by thesame, with the parameters output by predictors 140 being indicated by146, and the parameters output by predictor 144 being indicated byreference sign 148. Just as residual signal 150 output by quantizers 116does, the prediction parameters 146 and 148 of predictors 140 and 144are received by data stream former 118 which, for example, in a losslessmanner codes all of this data into data stream 104.

Before describing the mode of operation of the encoder of FIG. 1 in moredetail below, reference is made to FIG. 2 which shows the correspondingdecoder. Substantially, the decoder 200 corresponds to that part ofencoder 100 which, for each component, extends from dequantizer 124 topredictor 122 and accordingly, the same reference signs, but increasedby 100, are used with respect to these corresponding elements. To bemore precise, the decoder 200 of FIG. 2 is configured to receive thedata stream 104 at the input of a data stream extractor 218 of decoder200, configured to extract from the data stream 104 the residual signals150 ₁ to 150 ₃ and all related coding parameters including predicationparameters 146 and 148. Corresponding to the encoder 100 of FIG. 1, thedecoder 200 of FIG. 2 is structured into parallel decoding paths 230,with one path per component of the multi-component picture, thereconstruction of which is indicated using reference sign 202 and thereconstructed component of which are output at the output of therespective decoding path as 206, 208 and 210. Due to quantizations, thereconstruction deviates from the original picture 102.

As already denoted above, the decoder paths 230 ₁ to 230 ₃ of decoder200 substantially correspond to those paths of coding paths 130 ₁ to 130₃ of encoder 100, encompassing elements 124, 138, 126, 134, 128 and 122thereof. That is, the decoding paths 230 ₂ and 230 ₃ of the “dependentcomponents” 208 and 210 comprise between a respective output of datastream extractor 218 on the one hand and the respective output foroutputting the respective component 208 and 210, respectively, a serialconnection of a dequantizer 224, a spectral domain inter-componentprediction/residual recombiner 238, an inverse transformer 226, aspatial domain inter-component prediction/residual recombiner 234 andprediction/residual recombiner 228 connected between data streamextractor 218 on the one hand and the output of decoder 200 foroutputting multi-component picture 202, on the other hand, in the orderof their mentioning, wherein a predictor 222 is connected into afeedback loop leading from the prediction/residual recombiner 228 backto another input thereof. The further inputs of 238 and 234 are fed bythe respective spatial domain and spectral domain inter-componentpredictors 240 and 244. The decoding path 230 ₁ of the “base component”206 differs in that elements 238, 234, 244 and 240 are not present.Predictor 244 ₃ has an input thereof connected to an output ofdequantizer 224 ₂, and another output connected to the output ofdequantizer 224 ₁, predictor 240 ₃ has a first input connected to anoutput of inverse transformer 226 ₂ and another input connected to anoutput of inverse transformer 226 ₁. Predictor 244 ₂ has an inputconnected to the output of dequantizer 224 ₁, and predictor 240 ₂ has aninput thereof connected to inverted transformer 226 ₁.

It should be noted that predictors 140 ₃ and 140 ₂ of FIG. 1 have beenshown as being connected to the not-yet quantized residual signals ofunderlying components in the spatial domain merely for the sake of aneasier illustration, but that, as becomes clear from FIG. 2, in order toavoid prediction inconsistencies between encoder and decoder, predictors140 ₂ and 140 ₃ of FIG. 1 may alternatively and advantageously beconnected to the outputs of inverse transformers 126 ₂ and 126 ₁,respectively, instead of the non-quantized versions of the spectraldomain residual signals of the underlying components.

After having described the structure of both encoder 100 and decoder200, their mode of operation is described hereinafter. In particular, asalready described above, encoder 100 and decoder 200 are configured touse hybrid coding so as to encode/decode each component of themulti-component picture. Actually, each component of the multi-componentpicture 102 represents a sample array or picture, each spatiallysampling the same scene with respect to a different color component. Thespatial resolution of components 106, 108 and 110, i.e. the spectralresolution at which the scene is sampled with respect to the respectivecomponent, may differ from component to component.

As described above, the components of the multi-component picture 102are separately subject to hybrid encoding/decoding. “Separately” doesnot necessarily mean that the encoding/decoding of the components isperformed completely independent of each other. First of all,inter-component prediction removes redundancies between the componentsand additionally some coding parameters may be chosen commonly for thecomponents. In FIG. 3, for example, it is assumed that the predictors122 and 222 choose the same subdivision of picture 102 into codingblocks, but a component individual subdivision of picture 102 intocoding blocks by predictors 122 and 222 is feasible as well. Thesubdivision of picture 102 into coding blocks may be fixed or may besignaled within the data stream 104. In the latter case, subdivisioninformation may be part of prediction parameters output by predictor 122to data stream former 118 and indicated using reference sign 154,wherein data stream extractor 218 extracts these prediction parametersincluding the subdivision information and outputs same to predictor 222.

FIG. 3 illustrates exemplarily that the subdivision of picture 102 intocoding blocks or code blocks may be done in accordance with a two stageprocess, according to which the multi-component picture 102 is firstregularly subdivided into tree root blocks, the outlines of which areindicated using doubled lines 300 in FIG. 3, with subsequently applyingrecursive multi-tree subdivisioning in order to subdivide each tree rootblock 302 into code blocks 304, the outlines 306 of which areillustrated in FIG. 3 using simple continuous lines 306. Thus, codeblocks 304 represent leaf blocks of the recursive multi-treesubdivisioning of each tree root block 302. The aforementionedsubdivision information possibly contained within data stream 104—eitherfor the components commonly or for the components individually—maycomprise multi-tree subdivision information for each tree root block 302for signalling the respective tree root block's 302 subdivision into thecode blocks 304 and optionally subdivision information controlling andsignalling picture's 102 subdivision into the regular arrangement oftree root blocks 302 in rows and columns.

In units of code blocks 304, for example, predictors 122 and 222 varybetween a plurality of prediction modes supported by encoder 100 anddecoder 200, respectively. For example, predictors 122 ₁ to 122 ₃ selectthe prediction modes for the code blocks individually and indicate theselection via prediction parameters 154 ₁ to 154 ₃ to predictors 222 ₃.The available prediction modes may comprise temporal and spatialprediction modes. Other prediction modes may be supported as well, suchas inter-view prediction modes or the like. Using recursive multi-treesubdivisioning, such as dual-tree subdivisioning, code blocks may befurther subdivided into prediction blocks 308, the outlines 310 of whichare indicated in FIG. 3 using dashed lines. Respective recursivesubdivision information may be contained in the prediction parameters154 ₁ to 154 ₃ for each code block. In an alternative embodiment, thisselection of the prediction modes is performed at the granularity of theprediction blocks. Likewise, each code block 304 may, using recursivemulti-tree subdivisioning, such as dual tree subdivisioning, further besubdivided into residual blocks 312, the outlines of which are indicatedusing dash-dot-lines 314 in FIG. 3. Thus, each code block 304 is,concurrently, partitioned into prediction blocks 308 and residual blocks312. The residual blocks 312 may, optionally, be further subdivided intotransform blocks 316, the outlines of which are indicated usingdash-dot-dot lines 318 in FIG. 3. Alternatively, transform and residualblocks form the same entities, i.e. residual blocks are transform blocksand vice versa. In other words, the residual blocks may coincide withthe transform blocks in accordance with an alternative embodiment.Residual block and/or transform block related subdivision informationmay or may not be contained within the prediction parameters 154.

Depending on the prediction mode associated with the respective codeblock or prediction block, each prediction block 308 has respectiveprediction parameters associated therewith which are selected bypredictors 122 ₁ to 122 ₃ appropriately, inserted into parameterinformation 154 ₁ to 154 ₃ and used by predictors 222 ₁ to 222 ₃ so asto control the prediction within the respective prediction blocks 308accordingly. For example, prediction blocks 308 having a temporalprediction mode associated therewith may have a motion vector formotion-compensated prediction associated therewith, and optionally areference picture index indicating a reference picture from which, withthe displacement indicated by the motion vector, the prediction of therespective prediction block 308 is derived/copied. Prediction blocks 308of a spatial prediction mode may have a spatial prediction directionassociated therewith, contained within prediction information 151 ₁ to154 ₃, the latter indicating the direction along which the alreadyreconstructed surrounding of the respective prediction block isspatially extrapolated into the respective prediction block.

Thus, using the prediction modes and prediction parameters, predictors122 and 222 derive a prediction signal 120 ₁ to 120 ₃ for each of thecomponents, and for each of the components, this prediction signal iscorrected using a residual signal 156 ₁ to 156 ₃. These residual signalsare coded by use of transform coding. That is, transformers 114 ₁ to 114₃ perform a transformation, i.e. a spectral decomposition, onto eachtransform block 116 individually, such as a DCT, DST or the like, andthe inverse transformers 226 reverse the same individually for thetransform blocks 308, i.e. perform, for example, a IDCT or IDST. Thatis, as far as the encoder 100 is concerned, the transformers 114 performthe transformation onto the not yet quantized residual signal as formedby prediction residual formers 112. Inverse transformers 126 and 226reverse the spectral decomposition on the basis of the quantizedresidual signal 150 of the respective component which is in a losslessmanner, such as using Huffman or arithmetic coding, inserted into thedata stream by data stream former 118 and extracted therefrom using, forexample, Huffman or arithmetic decoding, by data stream extractor 218.

However, in order to lower the data rate for coding the residual signal256 ₁ to 256 ₃ using which the prediction signal 220 ₁ to 220 ₃ iscorrected at prediction/residual recombiners 228 ₁ to 228 ₃, encoders100 and 200 support inter-component prediction with respect to thecoding of the components' residual signal. As will be described in moredetail below, in accordance with embodiments of the present application,the inter-component prediction for coding the residual signal may beswitched on and off and/or forward and/or backwards adaptively adjustedat the granularity of residual blocks and/or transform blocks. Ifswitched off, the inter-component prediction signals output bypredictors 140, 144 and 240 and 244 are zero and the residual signals256 ₁ to 256 ₃ of all components are derived from the quantizedtransform coefficients contained in its respective residual signal 150 ₁and 150 ₃ solely. If switched on, however, inter-componentredundancies/correlations are removed as far as the dependent componentsare concerned, i.e. residual signals 256 ₂ and 256 ₃ are coded/decodedusing inter-component prediction. The base (first) component serving asinter-component prediction source is, as far as the inter-componentprediction is concerned, left unchanged. How this is done is outlined inthe following.

For the time being, the description of the inter-component redundancyreduction realized by predictors 140, 144, 240 and 244 focuses on theinter-component redundancy reduction between components 106 and 108 and206 and 208, respectively. After that, in order to ease understanding,the description is extended to the three component case illustrated inFIGS. 1 and 2.

As will become clear from the description brought forward below, theembodiments outlined below take advantage of, for example, the residualcharacterization of the chroma components, especially in cases whereabsolute chroma components, or planes, serve as the input. In case ofthe three components of FIGS. 1 and 2, for example, representingcomponents of a luma/chroma color space, component 106/206 may forexample be a luma component, while components 108/208 and 110/210 arechroma components, such as blue- and red-related chroma components. Bykeeping the distortion calculation defined over the original inputspace, the embodiments outlined below enable higher fidelity. In otherwords, the encoder of FIG. 1 along with the decoder of FIG. 2 enableinputting an original multi-component picture as it is without, forexample, any color space transformation being performed in advance. Thecoding efficiency achievable by the embodiments of FIGS. 1 and 2 isindependent from the input color space, i.e. the embodiments outlinedbelow for performing inter-component redundancy removal act as anadditional correlation removal step for y′CbCr input 106 to 110, and asa color transform in case of R′G′B′ input 106 to 110. Additionally, theembodiments further outlined below apply the redundancy reductionbetween the components, or planes, locally, i.e. the encoder 100 decidesfor each region of the image/picture 102, or the video, adaptivelywhether inter-plane/component prediction involving the residual signals,is applied or not. However, again it is noted that embodiments of thepresent invention are not restricted to color components or planes only,rather the techniques set out herein can be applied to genericplanes/components as well where the resulting residuals of the two ormore planes consists of correlation. For example, the embodimentsdescribed in the present application can be applied to planes fromdifferent layers in a scalable video compression scheme as well. On thetop of the prediction, the processing order of the components or planescan be chanted locally, such as for example by way of a syntax elementsignalling the component order in the bit stream. This alternative isalso described below.

With respect to FIGS. 1 and 2, a case of a hybrid block-based image andvideo compression scheme is illustrated, where the prediction performedby predictors 122/222 is performed log-based and transform coding towhich transformers 114, quantizers 116, data stream inserter 118 as faras the encoding side is concerned, and inverse transformer 226 anddequantizer 224 as well as data stream extractor 218, as far as thedecoding side is concerned, contribute is applied to the predictionerror, i.e. the output of prediction residual formers 112, referred toas residual.

Please note that the term block shall be understood as describing ageneric rectangular shape in the following, i.e. a block can have arectangular shape.

In the embodiments described next, the encoder decides on theapplication of the inter-claim/component prediction for each predictionblock 308 or transform block 304.

As an intermediate note, however, it is submitted herewith thatembodiments of the present invention are not restricted to the caseoutlined with respect to FIGS. 1 and 2, where the inter-plane/componentprediction is applied to the prediction residual of a spatially,temporally and/or inter-view prediction signal. Theoretically, theembodiments presented herein could likewise be transferred onto a casewhere the inter-plane/component prediction is performed on the sample ofthe components directly. In other words, when prediction itself isskipped, the original samples of the input signal should be referred to,or may be treated as, residual for the remaining description.

For each residual block 312 (or rectangular shape), in accordance withan embodiment, a syntax element is transmitted in the data stream 104,and the syntax element denotes whether or not the inter-plane/componentprediction by way of predictors 140, 144, 240, 244 should be used. Inthe case of a video compression scheme like H.265/EVC, also illustratedin FIG. 3, where the residual is further divided into smaller transformblocks or shapes 216, the encoder 100 may, in accordance with anembodiment, transmit the just mentioned syntax element specifying theusage or non-usage of the inter-plane/component prediction for eachtransform block 316, or even a group of transform blocks. Note that thegrouping, i.e. signalling level, could be adaptively selected and such agrouping decision may be transmitted as a further syntax element in thebit/data stream 104, such as in a header of the data stream. At thehighest signalling level the usage, or the non-usage of theinter-plane/component prediction might be signaled for a coding unit orcoding block 304, a group of code blocks 304, or even for a whole imageor frame.

Differently speaking, reference is made to FIG. 4. FIG. 4 illustrates areconstruction module 400 which is embodied in the embodiments shown inFIGS. 1 and 2 at several portions, namely per pair of

-   -   spatial domain inter-component predictor 140 ₂ and associated        spatial domain inter-component prediction/residual recombiner        134 ₂, receiving x in form of the data stream extracted,        dequantized and inverse transformed residual signal 156 ₁,        receiving y in form of the data stream extracted, dequantized        and inverse transformed residual signal 156 ₂, and outputting z        as residual signal 156′₂ replacing residual signal 156 ₂,    -   spectral domain inter-component predictor 144 ₂ and associated        spectral domain inter-component prediction/residual recombiner        138 ₂, receiving x in form of the data stream extracted and        dequantized residual signal 170 ₁, receiving y in form of the        data stream extracted and dequantized residual signal 170 ₂, and        outputting z as residual signal 170′₂ replacing residual signal        170 ₂,    -   spatial domain inter-component predictor 140 ₃ and associated        spatial domain inter-component prediction/residual recombiner        134 ₃, receiving x in form of the data stream extracted,        dequantized and inverse transformed residual signal 156 ₁ or the        data stream extracted, dequantized and inverse transformed        residual signal 156 ₂ (or any combination thereof or both of        them), receiving y in form of the data stream extracted,        dequantized and inverse transformed residual signal 156 ₃, and        outputting z as residual signal 156′₃ replacing residual signal        156 ₃,    -   spectral domain inter-component predictor 144 ₃ and associated        spectral domain inter-component prediction/residual recombiner        138 ₃, receiving x in form of the data stream extracted and        dequantized residual signal 170 ₁ or the data stream extracted        and dequantized residual signal 170 ₂ (or any combination        thereof or both of them), receiving y in form of the data stream        extracted and dequantized residual signal 170 ₃, and outputting        z as residual signal 170′₃ replacing residual signal 170 ₃,    -   spatial domain inter-component predictor 240 ₂ and associated        spatial domain inter-component prediction/residual recombiner        234 ₂, receiving x in form of the data stream extracted,        dequantized and inverse transformed residual signal 256 ₁,        receiving y in form of the data stream extracted, dequantized        and inverse transformed residual signal 256 ₂, and outputting z        as residual signal 256′₂ replacing residual signal 256 ₂,    -   spectral domain inter-component predictor 244 ₂ and associated        spectral domain inter-component prediction/residual recombiner        238 ₂, receiving x in form of the data stream extracted and        dequantized residual signal 270 ₁, receiving y in form of the        data stream extracted and dequantized residual signal 270 ₂, and        outputting z as residual signal 170′₂ replacing residual signal        270 ₂,    -   spatial domain inter-component predictor 240 ₃ and associated        spatial domain inter-component prediction/residual recombiner        234 ₃, receiving x in form of the data stream extracted,        dequantized and inverse transformed residual signal 256 ₁ or the        data stream extracted, dequantized and inverse transformed        residual signal 256 ₂ (or any combination thereof or both of        them), receiving y in form of the data stream extracted,        dequantized and inverse transformed residual signal 256 ₃, and        outputting z as residual signal 256′₃ replacing residual signal        256 ₃,    -   spectral domain inter-component predictor 244 ₃ and associated        spectral domain inter-component prediction/residual recombiner        238 ₃, receiving x in form of the data stream extracted and        dequantized residual signal 270 ₁ or the data stream extracted        and dequantized residual signal 270 ₂ (or any combination        thereof or both of them), receiving y in form of the data stream        extracted and dequantized residual signal 270 ₃, and outputting        z as residual signal 270′₃ replacing residual signal 270 ₃,

At all of these occasions at FIGS. 1 and 2, the subsequently describedin more detail inter-plane/component prediction is performed and at anyof these occasions, the embodiments of FIGS. 1 and 2 may be amended byway of the more generalized inter-plane/component prediction module 400of FIG. 4. Note that merely some of the occasions may actually be used.

As is shown in FIG. 4, the inter-plane/component prediction module 400or reconstruction module 400 has two inputs and one output and,optionally, uses a prediction parameter signalling between encoder anddecoder side. The first input 402 is denoted as “x” and represents theinbound reconstructed first component signal on the basis of which theinter-plane/component redundancy reduction for the second component isperformed by reconstruction module 400. This reconstructed firstcomponent signal 402 may be, as is shown in FIGS. 1 and 2, thetransmitted residual signal as extracted from the data stream for theportion of the first component, co-located to the portion of the secondcomponent being currently the subject of inter-plane/componentredundancy reduction, in spatial or spectral domain.

The other input signal 404 of reconstruction module 400 is denoted “y”and represents the transmitted residual signal of the portion of thesecond component, currently being the subject of inter-plane/componentredundancy reduction by module 400, in the same domain as signal 402,i.e. spectral or spatial domain. The reconstruction module 400reconstructs a second component signal 406, denoted “z” in FIG. 4 in,again, the same domain, which component signal 406 represents the mainoutput of reconstruction module 400 and at least participates inreconstructing the dependent component of the multi-component picture byreplacing x. “At least” means that, as shown in FIGS. 1 and 2, thecomponent signal 406 output by reconstruction module 400 may represent aprediction residual, and accordingly still have to be combined with theprediction signal 154, of the respective dependent component i.

Just as the other modules of encoder and decoder, the reconstructionmodule 400 operates on a block-basis. The operation on a block-basismay, for example, manifest itself in a block-wise adaptation of theinter-component redundancy reduction reversal performed byreconstruction module 400. The “block wise adaptation” may involve,optionally, the explicit signalling of prediction parameters 146/148within the data stream. A backward adaptive setting of the parametersfor controlling the inter-component redundancy reduction is feasible,however, as well. That is, referring to FIG. 4, in case of thereconstruction module 400 being built into the decoder, the predictionparameters enter the restriction module, and thus represent a furtherinput thereof, whereas in the case of reconstruction module 400 beingbuilt into the encoder, the prediction parameters are internallydetermined in a manner exemplified below involving, for example, thesolving of an LSE optimization problem.

As outlined in more detail below, a reconstruction module 400 may, forexample, operate in such a manner that z is representable as φ(αx+β+γy).α, β and γ are possible inter-component prediction parameters. For eachof α, β and γ, it may hold true that same is a constant, thus is neitherbackward nor forward adaptively varied, is backward adaptively variedand accordingly does not form part of the data stream, or is forwardadaptively varied and is signaled in the data stream. FIG. 5 illustratesthis for the exemplary case of the inter-component prediction form firstcomponent 106 to second component 108. IN specifically outlined examplesbelow, for example, the operation is eleviated in a manner so thatz=αx+y.

FIG. 5 shows a currently reconstructed portion or block 440 of thesecond component 108. FIG. 5 also shows the spatially correspondingportion/block 442 of the first component 106, i.e. the portion spatiallyco-located within the picture 10. The input signals 402 and 404 whichmodule 400 receives for components 106 and 108 with respect toco-located blocks 440 and 442 may, as outlined with respect to FIGS. 1and 2, represent residual signals as transmitted for components 106 and108 within the data stream. With respect to the second component 108,module 400 computes z. For each block, such as block 440, the parametersα, β and γ—or merely a subset thereof—are adapted in a mannerexemplified further below.

In particular, for a given block such as block 440, it may be signaledwithin the data stream by way of a syntax element, as to whether or notinter-component prediction is to be performed. The parameters α, β and γin case of inter-component prediction being switched on, merelyrepresent possible examples. For a block 440 for which inter-componentprediction is applied, a prediction mode may be signaled in the datastream, a prediction source may be signaled in the data, a predictiondomain may be signaled in the data stream and parameters related to theaforementioned parameters may be signaled in the data stream. Themeaning of “prediction mode”, “prediction source”, “prediction domain”and “related parameters” will become clear from the description broughtforward below. In the examples described so far, the inter-componentprediction operates on residual signals. That is, x and y wereprediction residuals as transmitted within the data stream and bothrepresent prediction residuals of a hybrid prediction. As also describedabove, x and y may be prediction residuals in the spatial domain or inthe frequency domain in the exemplary case of using transform coding asoutlined above. Applying the prediction in the stage of an encoder or adecoder has several benefits. First of all, additional memory is usuallyunnecessary, and second the inter-component prediction can be performedlocally, i.e. without the introduction of additional intermediate stepsafter the parsing process from the decoder point of view. In order todistinguish the prediction domain, a further syntax element might betransmitted in the bit stream. That is, the latter further syntaxelement may indicate whether the inter-component prediction domain maybe the spatial domain or the spectral domain. In the first case, x, yand z are in the spatial domain, and in the latter case x, y and z arein the spectral domain. Please note that from the decoder perspective,the residual is reconstructed from the bit stream and can be differentfrom those that have been generated in the encoder before thequantization step. However, it is advantageous to use the alreadyquantized and reconstructed residual as a prediction source in anencoder implementing the embodiment of the present application.Furthermore, in the case of skipping the transform stage, theinter-component prediction in the spatial and frequency domains isexactly the same. For such a configuration, the signalling of theprediction domain, i.e. spatial or frequency domain, can be skipped.

As far as the aforementioned “prediction modes” are concerned, same canbe affine, linear, non-linear or more complex. In the first case, thepredictor might be written as already described above, namely asz=φ(αx+β+γy) where z is the reconstructed residual signal or sample, xis the vector containing samples from the prediction source signal, α, βand γ are model parameters, and y samples from the current signal, i.e.the past residual signal from the decoder side, and φ can be some linearor non-linear function.

To keep the processing chain as simple as possible, an exampleconfiguration might keep the processing of the first component, such asthe luma component, unchanged and use the luma reconstructed residualsignal as a predictor for the component residual signals. This is apossible prediction source configuration and note that such a simpleprediction source simplifies the generic transformation approach, whereall three components or planes of the input signal may be used in orderto generate the transform samples.

Another possible configuration is to make the prediction sourceadaptive, i.e. signalling which residual signal of all alreadyavailable, or respectively reconstructed residual components, are usedfor prediction. Alternatively, the processing order can be changedlocally, e.g. the second component is reconstructed first and is used asprediction source for the remaining components. Such a configurationtakes the advantage from the fact that the delta between two componentsusing a bijective (or nearly invertible) predictor is the same, but withinverted sign, however, the absolute cost for coding the predictionsource is different. Furthermore, the combination of several predictionsources is possible. In this case, the combination weights might betransmitted in the bit stream or estimated backward-driven using thestatistics of the available or respective coded neighbours.

The specification of the model parameters can be performedbackward-driven, composed of backward-drive estimation and forwardsignalization, or completely forward signalized in the data stream. Anexample configuration is to use a fixed set of model parameters, knownboth at the encoder and decoder, and signalling the set index to thedecoder for each block or shape. Another configuration is to use adynamic set or a list where the order of predictors is changed after aspecific number of block or shapes. Such an approach enables higherlocal adaptation to the source signal. A more detail example onprediction mode, prediction source, prediction domain and parametersignalling is brought forward below.

As to the prediction mode, the following may be noted.

The prediction mode can be affine, non-linear, or a more complexfunction realized by approaches like splines or support vectorregression.

Note that color space transformations are mostly linear employing allavailable input components. That is, color space transformations tend tomap a three component vector of three color components, onto anothervector of another three components of another color space. Encoder anddecoder may, in accordance with an embodiment of the presentapplication, operate independently from the input color space, and hencethe luma component might be kept unchanged in order to form a predictionsource. However, in accordance with an alternative embodiment, thedefinition of the “luma component” or “first component” can be differentfor each block, such as prediction or transformation block (orrectangular shape), i.e. for each block or shape, the component whichserves as the “first component” might be selected adaptively. Theadaptation may be indicated to the encoder by a signalling in the datastream. For example, while FIG. 5 illustrates the case of component 106forming the “first component” while component 108 is the componentinter-component predicted, i.e. the second component, as far as block440 is concerned, things could be different for another block of picture10 where, for example, component signal 106 is inter-component predictedfrom component 108. The block-wise adaptation of the “prediction source”may be indicated within the data stream as just-outlined. Additionallyor alternatively, for each block 440, a syntax element signalling wherethe prediction is applied or not may be transmitted within the datastream. That is, in case of using component 106 as the “first component”constantly, such a syntax element would be present for blocks of adependent component only, i.e. components 108 and 110 in FIGS. 1 and 2.In that case, the first component, such as the luma component, wouldprovide the prediction source, namely the residual signal thereof incase of the above outlined embodiments.

If prediction is enabled for a certain block 440, additionally oralternatively the prediction mode may be signaled within the data streamfor that block 440. Please note that the prediction might be skipped forthe case of a zero-valued reconstructed first component signal, i.e. azero-valued residual luma signal in case of using a prediction residualas a basis for the inter-component prediction. In that case, theaforementioned syntax element signalling whether or not theinter-component prediction is applied, could be omitted, i.e. notpresent, in the data stream for the respective block 440.

In the case of a combined backward-driven and forward signalizationapproach, parameters derived from already coded respective reconstructeddata can serve as starting parameters. In such a case, a delta relativeto the selected prediction mode can be transmitted in the data stream.This could be achieved by calculating the optimal parameter for a fixedor adapted prediction mode and the calculated parameters are transmittedin the bit stream. Another possibility is to transmit some deltarelative to a starting parameter derived by using a backward-driveselection approach or using the parameters calculated and selected bythe backward-driven approach only.

An example configuration of prediction modes is described in thefollowing. In this example, the first prediction mode implies α=1, β=0,γ=1 and φ(x)=└x┘ and the second prediction mode implies the sameparameters except for α=0.5 with x=(x₀), y=(y₀) and the single elementsof x and y are the residual value for the block at the same spatialposition in the first and second components, such as in the lumacomponent and the respective position at the chroma component.Differently speaking, in accordance with an embodiment of the presentapplication, for each block 440, for which the inter-componentprediction is applied, it is signaled in the data stream whether aequals a first value, namely 1, or a second value, here 0.5. Instead ofa signalling in the data stream, a mixed backward and forward drivenapproach may be used as already described above, or the selection amongthe available values of α may be performed backward adaptively. β and γwould merely represent constants.

Note that the single element in y is replaced after the prediction by z.In other words, the reconstruction module 400 receives the correctionsignal 404 and replaces same by z 406. Also note that when using such aconfiguration, the inter-component prediction is simplified to anaddition operation: either the fully reconstructed residual sample valueof the first component (α=1) or half its value (α=0.5) is added to acorrection sample value 404. The halving may be generated by a simpleright shift operation. In that case, for example, the configurationcould be implemented by realizing the multiplication between x and α inthe predictor within reconstruction module 400, and realizing theaddition in the adder shown in FIG. 4. In other words, in the givenexample, at the encoder side the mode of operation would be as follows.

The residual signal of the chroma component for a transform block (orrectangular shape) is subtracted by the reconstructed residual sample atthe same (spatial or frequency) location in the luma plane. Aftertransform and quantization, the reconstructed residual is added to thereconstructed residual sample at the same spatial location in the lumaplane. From the decoder perspective, only the latter operation may beused. An example configuration of an approach involving abackward-driven scheme can be done as follows. For each block or shape440, an optimum parameter α is calculated. A starting α⁰ is derivedbackward-driven from the local neighbourhood, e.g., from the above andthe left block (or rectangular shape) that have been coded before. If asyntax element in the bit stream signals that no further parameters aretransmitted in the bit stream, the derived α⁰ is used. Otherwise, i.e.,prediction should be used but corrected by a syntax element denotes adelta α⁰ in the bit stream. It is also possible to transmit two flags,the first flag indicates whether α⁰ should be used and the second flagindicates whether an α⁰ exists in the bit stream.

Another possible configuration is to increase the granularity for theparameter derivation process. This approach also implies highersignalization granularity when forward transmission is applied.Otherwise, a higher granularity for the backward-driven scheme isimplied. In this possible configuration, the prediction parameters arederived for each sample or for a group of samples within a transformblock (or rectangular shape) or even for a prediction block itself.Please note that a special case is given by coupling the signallinglevel to transform blocks (or rectangular shapes). For the currentsample or group of samples, a specific amount of samples within the sametransform block or prediction block, defined by a predefined window, istaken for the parameter derivation. Using the above example where anaffine predictor is employed, the parameter an can be derived frompreviously reconstructed sample or group of samples as follows where nis the group index.

z _(n)=φ(α_(n-1) x+β _(n-1)+γ_(n-1) y)

The parameter for the first sample or group of samples can beinitialized by some default values or calculated from neighbouringblocks or shapes. Another possibility is to transmit the optimumparameters for the first sample or group of samples. In order to use asmuch previous samples as possible, a predefined scan pattern can be usedto map the 2-dimensional residual block (or rectangular shape) to an1-dimensional vector. For example, the samples or the groups of samplescan be scanned vertically, horizontally, or directional similar to thescan directions of the transform coefficients. Again, the specific scancan be derived by a backward-driven scheme or it's signaled in the bitstream.

Another extension is the combination of the already presented exampleand a transformation using all three available components as input.Here, in this example, the residual signal is transformed using atransformation matrix that removes the correlation for the giventransform block. This configuration is useful when the correlationbetween the planes is very large or extremely small. An exampleconfiguration would use Y′CoCg transformation in the case of input colorspaces like R′G′B′ or a principal component analysis approach. For thelatter case, the transform matrix has to be signaled to the decoder in aforward manner or using a predefined set and rule known at encoder aswell as decoder to derive the matrix values. Please note that thisconfiguration may use the residual signal of all available components orplanes.

As to the prediction domain, the following is noted.

The prediction domain can be, as described above, the spatial domain,i.e., operating on the residual, or frequency domain, i.e., operating onthe residual after applying a transformation like DCT or DST.Furthermore, the domain can be a composition of both by transmitting theinformation to the decoder. In addition to the domain for theprediction, parameters related to the domain can be transmitted orderived by a backward-driven scheme.

Related to the domain parameters is an additional sub sampling of thechroma component, i.e., a chroma block (or rectangular shape) is scaleddown horizontally, vertically, or both. In such a case, the predictionsource might be down sampled as well or a set of prediction mode has tobe selected that consider different resolution in spatial domain,frequency domain, or both. Another possibility is to upscale theprediction target so that the dimension of the prediction source and theprediction target match each other. The downscaling further improves thecompression efficiency, especially for very flat areas in the image orvideo. For example, the prediction source contains both low and highfrequencies but the chroma block (or rectangular shape) contains of lowfrequencies only. In this example, the sub sampling of the predictionsource would removes the high frequencies and a less complex predictionmode can be employed and connected to that less information has to betransmitted to the decoder. Please note that the signalling of adownscaling usage might be done for each transform block, or for eachprediction block, or even for a group of prediction blocks or for thewhole image.

In addition to the additional down sampling approach, a bit depthadjustment might be transmitted to the decoder too. This case occurswhen the precision of the samples are different along the differentcomponents. One possible way is to reduce or increase the number of bitsfor the source. Another possible configuration might increase ordecrease the bit depth of the target and corrected the final result backto the correct bit depth. A further option is the usage of a set ofpredictors suitable for the different bit depth. Such a prediction modewould consider the different bit depth by the prediction parameters. Thesignalling level for the bit depth correction can be done for each blockor shape, or for the whole picture or sequence, depending on thevariation of the content.

As the prediction source, the following is noted.

The prediction source can be the first component or all availablecomponent. For each block (or rectangular shape), the prediction sourcemight be signaled by the encoder. Alternatively, the prediction sourcecan be a dictionary contains all possible blocks, whether prediction ortransform block, from all available components and the prediction sourcethat should be used for the prediction is signaled to the decoder by asyntax element in the bit stream.

As to the parameter derivation, the following is noted.

The parameters may, exemplarily, derived from the causal neighbourhoodof the block—in the decoder so as to perform the elsewhere mentionedbackward adaptivity or in the encoder, so as to signal the result in thedata stream so as to drive the decoder in a forward-adaptive manner—bysolving a least square error (LSE) optimization problem. The LSE can beformulated as:

$\min\limits_{\alpha,\beta,\gamma}{{z - {\phi \left( {{\alpha \; x} + \beta + {\gamma \; y}} \right)}}}^{2}$

Minimizing this equation with respect to α. The parameter for theequation has a closed form solution calculated as:

$\alpha = {\frac{A_{1}}{A_{2}}\mspace{14mu} {where}}$A₁  is  the  covariance  between  z  and  ϕ(α x + β + γ y), and  A₂is  the  variance  of  z.

An Integer implementation is implemented for this method to replace thedivision operation by a lookup table and a multiplication operation. A₂is descaled in order to reduce the table size while A₁ is descaled inorder to avoid multiplication overflow. Only the most significant bitsn_(A) ₁ and n_(A) ₂ are kept from A₁ and A₂. A′₁ and A′₂ can be derivedas:

A′=[A>>r _(A) ]<<r _(A)

where

r _(A)=max(bd(A)−n _(A),0)

Where bd(A) is the bitdepth of the value of A calculated by log₂ A.Now α′ can be recalculated as

${\alpha^{\prime} \approx \frac{\left\lbrack {A_{1}r_{A_{1}}} \right\rbrack r_{A_{1}}}{\left\lbrack {A_{2}r_{A_{2}}} \right\rbrack r_{A_{2}}}n_{\alpha}} = {\frac{\left( {1n_{table}} \right) \cdot \left\lbrack {\left\lbrack {A_{1}r_{A_{1}}} \right\rbrack \left( {r_{A_{1}} + n_{\alpha}} \right)} \right\rbrack}{\left\lbrack {A_{2}r_{A_{2}}} \right\rbrack \left( {r_{A_{2}} + n_{table}} \right)} = {\quad{\left\lbrack \frac{\left( {1n_{table}} \right)}{\left\lbrack {A_{2}r_{A_{2}}} \right\rbrack} \right\rbrack \cdot \left\lbrack {\left\lbrack {A_{1}r_{A_{1}}} \right\rbrack \left( {r_{A_{1}} + n_{a} - r_{A_{2}} - n_{table}} \right)} \right\rbrack}}}$

Now the division can be represented by a lookup table

$\left\lbrack \frac{\left( {1n_{table}} \right)}{\left\lbrack {A_{2}r_{A_{2}}} \right\rbrack} \right\rbrack$

whose elements are represented by n_(table) bits. The index for thistable is calculated as [A₂>>r_(A2)] and the table size is n_(A2).

Please note that in the above minimization problem, y represents theresidual signal which, for the respective inter-component predictedblock 440, is losslessly transmitted within the data stream. In otherwords, y is the correction signal for the inter-component predictedblock 440. Same may be determined iteratively with, in each iteration,performing the solving of the above outlined LSE optimization problem.In this manner, the encoder may optimally decide on performing or notperforming inter-component prediction, in choosing the inter-componentprediction parameters such as prediction mode, prediction source and soforth.

As to the parameter signalling, the following is noted.

The prediction itself might be switchable and a header flag specifyingthe usage of the residual prediction should be transmitted in thebeginning of the bit stream. When prediction is allowed, a syntaxelement specifying its local usage is embedded in the bit stream for ablock 440, which as described before may be a residual block (orrectangular shape), a transform block (or rectangular shape), or even agroup of transform blocks (or rectangular shapes). The first bit mightdenote whether the prediction is enabled or not and the following bitsmight denote the prediction mode, the prediction source, or theprediction domain and the related parameters. Please note that onesyntax element can be used to enable or disable the prediction for bothchroma components. It is also possible to signal the usage of theprediction as well as prediction mode and source for each second (e.g.chroma) component separately. Again, in order to achieve a highadaptation to the residual signal, a sorting criterion might be used tosignal the prediction mode. For example, the most used prediction modeis one, then a sorted list would contain the mode one at index zero.Only one bit may then be used for signalling the most probable mode one.Furthermore, the usage of the prediction might be restricted In the caseof applying the inter-component prediction on residuals, the correlationmight be high if the same prediction mode for generating the residual isused among the different colour components. Such a restriction is usefulin intra predicted blocks (or rectangular shapes). For example, thisinter-component prediction can be applied only if the same intraprediction mode as used for block (or rectangular shape) 442, which maybe luma, is used for the block (or rectangular shape) 440, which may bechroma.

That is, the in the latter case, the block-wise adaptation of theinter-component prediction process would involve checking whether block440 is associated with a spatial prediction mode as far as theprediction by predictor 222 ₂ is concerned, and whether the spatialprediction mode coincides, or does not deviate by more than apredetermined amount, from the spatial mode using which the co-locatedblock 442 is predicted by predictor 222 ₁. The spatial prediction modemay, for example, comprise a spatial prediction direction along whichalready reconstructed samples neighbouring block 440 and 442,respectively, are extrapolated into block 440 and 442, respectively, inorder to result in the respective prediction signal 220 ₂ and 220 ₁,respectively, which is then combined with z and x, respectively.

In an embodiment, the prediction source is the luma component. In thisadvantageous embodiment, which is depicted in FIGS. 1 and 2 if theinterconnections between components 108/208 and 110/210 are left off,the processing of the luma is unchanged and the resulting reconstructedresidual of the luma plane is used for prediction. As the consequence,the prediction source is not transmitted in the bit stream.

In another embodiment, the prediction source is transmitted for a Iblock or shape 440, such as a residual block, a group of residual blocksor shapes, e.g., for the size where the intra or inter prediction isapplied.

For example, the prediction source is luma for the first chromacomponent and luma or the first chroma component for the second chromacomponent. This advantageous embodiment is similar to a configurationallowing all available planes as prediction source and corresponds toFIGS. 1 and 2.

To illustrate the aforementioned embodiments, see FIG. 6. Athree-component picture 102/202 is shown. The first component 106/206 iscoded/decoded using hybrid (de)coding without any inter-componentprediction. As far as the second component 108/208 is concerned, same ispartitioned into blocks 440, one of which is exemplarily shown in FIG. 6just as it was the case in FIG. 5. In units of these blocks 440, theinter-component prediction is adapted with respect to, for example, a asit was described above. Likewise, picture 102/202 is partitioned intoblocks 450 as far as the third component 110/210 is concerned with onesuch block being representatively shown in FIG. 6. As described withrespect to the just outlined two alternatives, it may be that theinter-component prediction of block 450 is performed by using the firstcomponent 106/206 as a prediction source inevitably, i.e. the co-locatedportion 452 of the first component 106/206. This is indicated usingcontinuous-lined arrow 454. In accordance with a second alternative justdescribed, however, a syntax element 456 in the data stream 104 switchesbetween using the first component as the prediction source, i.e. 454,and using the second component as the prediction source, i.e.inter-component predicting block 450 on the basis of the co-locatedportion 458 of the second component 108/208 as indicated by arrow 460.In FIG. 6, the first component 106/206 may be, for example, the lumacomponent, whereas the other two components 108/208 and 110/210 may bechroma components.

It is noted that with respect to FIG. 6 that, possibly, the partitioninginto blocks 440 for the second component 108/208 may be signaled withinthe data stream 104 in a manner independent from, or allowing adeviation from, partitioning of component 110/210 into blocks 450.Naturally, the partitioning could be the same as well and could even beadopted from the one signaled form, or used for, the first component asit is the exemplary case in FIG. 10 described later.

A further embodiment, which was just outlined above, is the possibilitythat all components of picture 110/210 may, alternately, serve as aprediction source. See FIG. 7. In FIG. 7, all components 106 to 110/206to 210 have a common partitioning into blocks 470 associated therewithwith one such block 470 being exemplarily illustrated in FIG. 7. Thepartitioning or subdivision into blocks 470 may be signaled within thedata stream 104. As already stated above, block 470 may be residual ortransform blocks. Here, however, any component may form the “firstcomponent”, i.e. the prediction source. A syntax element 472 and a datastream 104 indicates for block 470 as to which among components 106 to110/206 to 210 forms the prediction source for, for example, the othertwo components. FIG. 7, for example, illustrates another block 472, forwhich the prediction source is chosen differently as illustrated by thearrows in FIG. 7. Within block 470, the first component serves as theprediction source for the other two components, in the case of block 472the second component assumes the role of the first component.

With respect to FIGS. 6 and 7, it is noted that the scope at which thesyntax elements 456 and 472 indicate the prediction source may be chosendifferently, i.e. for each block 450 and 470/72 individually, or forgroups of blocks or even the whole picture 102/202.

In a further embodiment, the prediction source can be all availablecomponent or a subset of the available component. In this advantageousembodiment, a weighting of the source may be signaled to the decoder.

In an advantageous embodiment, the prediction domain lies in the spatialdomain. In this embodiment, the residual for a whole residual block orshape might be used or only a specific part of the residual block orshape, depending on the signalling configuration. The latter case isgiven when the prediction is signaled individually for each transformblock or shape and a further subdivision of residual blocks or shapesinto smaller transform blocks or shapes are allowed.

In a further embodiment, the prediction domain lies in the frequencydomain. In this advantageous embodiment, the prediction is coupled tothe transform block or shape size.

In a further embodiment, the prediction domain can be in the spatial orfrequency domains. In this embodiment, the prediction domain isspecified separately, either by forward signalization or backward-drivenestimation depending on the local statistics.

The latter circumstance is illustrated in FIG. 8. In FIG. 8, merely twocomponents of picture 102/202 are exemplarily shown. Further, acurrently inter-component predicted block 440 and its spatiallycorresponding portion 442 are shown as well as a syntax element 490contained in the data stream 104 so as to signal for block 440 whetherthe inter-component prediction by reconstruction module 400 implemented,for example, using the model involving function φ as discussed above, isperformed in transform domain or spatial domain. In particular, FIG. 8illustrates the processing in the decoder for illustration purposes.First of all, from the data stream 104, the correction signal of thesecond component 208 relating to block 440 is extracted from the datastream, and likewise a residual signal is extracted from the data stream104 for the first component 206 as far as the spatially correspondingportion 442 is concerned. If the syntax element 490 indicates for block440 the use of the spectral domain, these signals are input intoreconstruction module 400 directly with the inter-component predictedoutput z replacing the correction signal of block 440 for the furtherreconstruction of the second component 208 of picture 202. However, ifthe syntax element 490 indicates the usage of the spatial domain, thesignals extracted from the data stream 104 for block 440 and spatiallycorresponding portion 442 are subject to inverse transformation 226prior to the processing by reconstruction module 400. In the case ofusing the spectral domain, a combination of x and y, so as to obtain zis performed spectral-component-wise, and in the case of using thespatial domain, the combination of x and y so as to obtain z by module400 is performed sample-wise.

Again, the syntax element 490 may signal the domain to be used forinter-component prediction for block 440 individually, for groups ofblocks 440 or for the whole picture or for an even larger scope, such asa group of pictures.

In a further embodiment, both prediction domains are involved in theprediction process. In this advantageous embodiment of the invention, aprediction is made first in the spatial domain, and a further predictionis applied in the frequency domain with both predictions using differentprediction modes and sources.

In an embodiment, the chroma block or shape can be subsampledhorizontally, vertically, or both by some factors. In this embodiment,the down scale factor can be equal to the power of two. The usage of thedown sampler is transmitted as a syntax element in the bit stream andthe down sampler is fixed.

In a further embodiment, the chroma block or shape can be subsampledhorizontally, vertically, or both by some factors. The factor can betransmitted in the bit stream and the down sampler is selected from aset of filters, where the exact filter can be addressed by an indextransmitted in the bit stream.

In a further embodiment, the selected up sampling filter is transmittedin the bit stream. In this embodiment, the chroma blocks might beoriginally sub sampled, and hence, in order to use the prediction with amatching block or rectangle size, the up sampling has to be done beforeprediction.

In a further embodiment, the selected down sampling filter istransmitted in the bit stream. In this embodiment, the luma is downsampled in order to achieve the same block or rectangle size.

In an embodiment, a syntax element is signaled denoting the bitcorrection when the bit depth of the source and the target is different.In this embodiment, the luma precision can be decreased or the chromaprecision can be increased in order to have the same bit depth for theprediction. In the latter case, the chroma precision is decreased backto the original bit depth.

In an embodiment, the number of prediction modes is two and the set ofpredictors is defined exactly as in the given example.

In a further embodiment, the number of prediction mode is one and theconfiguration is the same as described in the previous embodiment.

In a further embodiment, the number of predictors is freely adjustablewith the set of predictors is defined exactly as in the given example.This embodiment is the more generic description of the example withα=1/m where m>0 denotes the prediction number or mode. Hence, m=0denotes that the prediction should be skipped.

In a further embodiment, the prediction mode is fixed, i.e., theprediction is enabled. For this embodiment, one might enable theadaptive inter-plane prediction and set the number of predictors equalto zero.

In a further embodiment, the prediction is applied and the predictionparameters like a are derived from the neighbouring blocks or shapes. Inthis embodiment, the optimum a for a block or shape is calculated afterthe full reconstruction. The calculated a acts as parameter for the nextblock or shape in the local neighbourhood.

In a further embodiment, a syntax element is transmitted in the bitstream indicating the usage of the parameters derived from the localneighbourhood.

In a further embodiment, the parameters derived from the neighbourhoodare used. In addition to that, a delta relative to the optimumparameters calculated in the encoder might be transmitted in the bitstream.

In a further embodiment of, the backward-driven selection scheme for theparameters are disabled and the optimum parameters are transmitted inthe bit stream.

In a further embodiment, the usage of the starting a as well as theexisting of a delta a in the bit stream is signaled separately.

In an embodiment, the signalling of prediction mode, prediction source,and prediction parameters are restricted to the same regular predictionmode. In this embodiment, the information related to the inter-planeprediction is transmitted only when the intra prediction mode for thechroma component is the same as used for the luma component.

In a further embodiment, the block is partitioned into windows ofdifferent sizes and the parameters for the current window are derivedfrom the reconstructed previous window within the block. In a furtherembodiment, parameters for the first window are derived fromreconstructed neighbouring blocks.

In a further embodiment of the, a syntax element is transmitted in thebit stream indicating the usage of the parameters derived from thelocally neighbourhood to be used for the first window.

In a further embodiment, the windows can be scanned in a vertical,horizontal or vertical direction.

In a further embodiment, the parameters for the current window arederived from the previous window where the previous window is decidedaccording to the scan position of the transform coefficients sub blocks.

In a further embodiment, the window scanning is limited to one scanningdirection.

In a further embodiment, the parameters are derived using an integerimplementation by using a lookup table and a multiplication operationinstead of a division.

In an embodiment, a global flag transmitted in the header of the bitstream denote the usage of the adaptive inter-plane prediction. In thisembodiment, the flag is embedded in the sequence level.

In a further embodiment, a global flag is transmitted in the header ofthe bit stream, with the embedment in the picture parameter level.

In a further embodiment, the number of predictors is transmitted in theheader of the bit stream. In this embodiment, the number zero denotesthat prediction is enabled, a number unequally to zero denote that theprediction mode is selected adaptively.

In an embodiment, the set of prediction mode is derived from the numberof prediction modes.

In a further embodiment, a set of prediction mode is known at thedecoder and the decoder specifying all model parameters of theprediction.

In a further embodiment, the prediction modes are all linear or affine.

In an embodiment, the set of predictors is hybrid, i.e., containingsimple prediction modes using other planes as prediction source, andcontaining more complex prediction modes using all available planes andtransform the input residual signals into another component or planespace.

In an embodiment, the usage of prediction is specified for eachtransform block or shape for each chroma component. In this embodiment,this information may be skipped when the luma component consists ofzero-valued residual at the same spatial location.

In an embodiment, the modes are transmitted using truncated unarydecomposition. In this embodiment, different context models are assignedfor each bin index, however, limited to a specific number, e.g., bythree. Furthermore, the same context models are used for both chromacomponents.

In a further embodiment, different chroma planes use different contextmodel sets.

In a further embodiment, different transform block or shape sizes usesdifferent context model sets.

In a further embodiment, the mapping of bins to prediction mode isdynamic or adaptively. In this embodiment, from decoder perspective, adecoded mode equal to zero denotes the most used mode up to the decodedtime.

In a further embodiment, the prediction mode, and the prediction sourceif using a configuration allowing different prediction sources, istransmitted for a residual block or shape. In this embodiment, differentblock or shape sizes may use different context models.

The embodiment described next, especially concerns an example for how tocode the prediction parameters for the “Cross Component Decorrelation”described so far.

Although not restricted thereto, the following description may bethought of as referring to the alternative where the dependent (second)component is reconstructed based on the reference (first) componentsignal x and the residual (correction) signal y via computing z=αx+ywith using z as the prediction of the dependent component signal. Theprediction may be applied in the spatial domain, for example. As in theexamples above, the inter-component prediction may be applied to ahybrid-coding residual signal, i.e. first and second component signalmay represent a hybrid coding's residual signal The following embodimentconcentrates, however, on the signalling of a: this parameter is codedin a sub-picture basis such as, for example, in units of residual blocksinto which the multi-component picture is subdivided. The following isabout the fact that the signal-able states of α should advantageouslyvariable, too, in order to account for the fact that the range ofoptimal values for α depend on the sort of picture content which, inturn, varies in scope/units larger than residual blocks. Thus, inprinciple, the details set out below with respect to the transmission ofα may be transferred to the other embodiments outlined above as well.

The cross-component decorrelation (CCD) approach utilizes the remainingdependency between different color components enabling highercompression efficiency. An affine model can be employed for such anapproach and the model parameters are transmitted in the bit stream asside information.

In order to minimize the side information cost, a limited set ofpossible parameters are transmitted only. For example, a possible CCDimplementation in High Efficiency Video Coding (HEVC) could use a linearprediction model instead of an affine prediction model and the only modeparameter, i.e., the slope or gradient parameter α, could be limited inthe range from 0 to 1 and be quantized non-uniformly. Particularly, thelimited set of values for a could be αε{0, ±0.125, ±0.25, ±0.5, ±1}.

The selection of such a quantization for the linear prediction modelparameter could be based on the fact that the distribution of a issymmetrically concentrated around the value 0 for natural video contentstored in the Y′CbCr color space. In the Y′CbCr, the color componentsare decorrelated by using a fixed transformation matrix to convert fromR′G′B′ before entering the compression stage. Due to the fact that aglobal transformation is often sub-optimal, the CCD approach can achievehigher compression efficiency by removing the remaining dependencybetween the different color components.

However, such an assumption does not hold true for different kind ofcontent, especially for natural video content stored in the R′G′B′ colorspace domain. In this case, the gradient parameter α is oftenconcentrated around the value 1.

Similar to the case given above, the distribution becomes completelydifferent when CCD is extended to the first chroma component as theprediction source. Hence, it may be beneficial to adjust the CCDparameters according to the given content.

For example, for Y′CbCr, the quantization of a can be set to (0, ±0.125,±0.25, ±0.5, ±1) while for R′G′B′ the quantization of a could beinverted, i.e. (0, ±1, ±0.5, ±0.25, ±0.125). However, allowing differententropy coding paths introduces additional issues. One problem is thatthe implementation becomes more expensive in terms of area and speed forboth hardware and software. In order to avoid this drawback, theparameter range can be specified in the picture parameter set (PPS)level where the usage of CCD is also indicated.

That is, a syntax element signalling α is transmitted at a sub-picturelevel/granularity, e.g. individually for a residual block. It could becalled res_scale_value, for example. It could be, for example, codedusing a (truncated) unary binarization combined with binary arithmeticcoding of the bin string. The mapping of the (non-binarized) values ofres_scale_value onto α could be implemented such that the mapping isvaried using the pps, i.e. for the complete picture or even at largerscope such as on a per picture sequence basis. The variation could varythe number of representable α values, the order of representable αvalues and the selection of representable α values, i.e. their actualvalues. Merely allowing for switching the order among the representableα values or restricting the representable α values to positive ornegative values only is one way to provide for content adaptivity, butthe embodiments outlined further below allow—by merely minor increasedoverhead—for an even increased flexibility in varying the mapping fromthe sub-picture granularly signalled res_scale_value to a values such asa variation of the size, members and member order of the mapping'sco-domain (representable set of α values), and it turned out that theadvantages provided by this provision in terms of bit savings fortransmitting res_scale_value overcompensates—seen over a typical blendof video contents coded in YCC or RGB—the necessity of signalling thevariation of the mapping.

The specification of the range for a can be done, for example, asfollows. In the case of Y′C_(b)C_(r), the advantageous sub-set can befor example (0, ±0.125, ±0.25, ±0.5) while it can be (0, ±0.5, ±1) or(0, 0.5, 1) or even (0, 0.5, 1, 2) for R′G′B′. In order to achieve thementioned behavior, the range can be specified in the PPS using twosyntax elements representing two values. Given the above example and thefact that the prediction is performed with 3 point accuracy, i.e. theprediction sample values are multiplied by a and then right-shifted by3, the range configuration for Y′CbCr can be transmitted as [−3, 3].

However, with such a signalling, only the second and the third case forR′G′B′ can be achieved using [2, 3] and [2, 4]. In order to achieve thefirst example for R′G′B′, the sign has to be separated using anadditional syntax. Furthermore, it is sufficient to transmit the deltafor the second value with the first value serves as the starting point.For this example, the second R′G′B′ configuration is [2, 1] instead of[2, 3].

In the case of prediction from the first chroma component, the rangevalues can be specified separately for each chroma component. Note thatthis can be done even without the support for the prediction from thefirst chroma component.

Given the limit specified in the PPS, the parsing and reconstruction ofthe prediction parameter α is modified as follows. For the case withoutlimit, i.e., αε{0, ±0.125, ±0.25, ±0.5, ±1} and a 3 point accuracyprecision, the final α^(F) is reconstructed as follows where α_(P)denotes the parsed value from the bit stream: α_(F)=1<<α_(P). This ismodified according to α_(F)=1˜˜(a_(P)+a_(L)) where a_(L) denotes theoffset for the smallest absolute value when the range lies completely inpositive or negative range.

Both values are used to derive the limit on the number of bins parsedfrom the bit stream when α_(P) is binarized using truncated unary code.Please note that the parsing of the sign might depend on the givenrange. A better way to utilize this aspect is to encode the sign beforethe absolute value of α. After the coding the sign, the number ofmaximum bins to be parsed from the bit stream can be derived. This caseis useful when the range is asymmetric, e.g., it is [−1, 3].

Often, a different order is desired like (0, 1, 0.5), e.g., for someR′G′B′ content. Such an inversion can be simply achieved by setting therange values according to [3, 2]. In this case, the number of binsparsed from the bit stream is still 2 (the absolute difference betweenthe two range values is n=1 and the number of bins in case of truncatedunary code is n+1). Then, the inversion can be achieved by two ways. Thefirst option introduces a fixed offset, which is equal to 2 times thecurrent value if no inversion is desired and the maximum representablevalue in the case of inversion. The second and more elegant way to dothis is to expand to range transmitted in the PPS to a memory and accessthe corresponding value through a look-up operation. This approach leadsto a unified logic and single path for both cases. For example, the case(0, 0.25, 0.5, 1) is signaled in the PPS by transmitting [1, 3] and amemory is created with the following entries (0, 1, 2, 3). On the otherway, i.e., in the inverted case with the transmitted values [3, 1] inthe bit stream, a memory is created with the following entries (0, 3, 2,1). Using such an approach, the final α_(F) can be formulated asα_(F)=1<<(LUT[α_(P)]) where LUT[α_(P)] denotes the look-up operation.

In order to explain the most recently mentioned aspect in more detail,reference is made to FIGS. 9 a, b and c. FIGS. 9 a, b and c, in thefollowing simply referred to as FIG. 9, exemplarily show onemulti-component picture 102/202 exemplarily in a layered manner: thefirst (reference) component 106/206 behind the dependent (second)component (108/208).

Picture 102/202 may be part of a video 500.

The data stream 104, into which picture 102/202 is coded, comprises ahigh-level syntax element structure 510 which relates at least to thewhole picture 102/202 or even beyond that to a picture sequence out ofvideo 500 which comprises picture 102/202. This is illustrated in FIG. 9using the curly bracket 502. Further, the data stream 104 comprises on asub-picture level, first-weight syntax elements. One such first-weightsyntax element 514 is exemplarily shown in FIG. 9 as pertaining to anexemplary residual block 440 of picture 102/202. The first-weight syntaxelement is for individually setting the first weight, i.e. a, ininter-component predicting the dependent component 108/208 on the basisof the co-located portion of reference component 106/206.

The first-weight syntax element is coded using a truncated unarybinarization. An example for such TU binarization is shown in FIG. 9 at518. As shown, such a TU binarization consists of a sequence of binstrings of increasing length. In the manner described above, thehigh-level syntax element structure 510 defines how the bin strings ofbinarization 518 are mapped onto possible values for α. An exemplary setof such possible values for a is shown in FIG. 9 at 520. In effect, thehigh-level syntax element structure 510 defines the mapping 522 from theset of bin strings 518 onto a subset of set 520. By this measure, it isfeasible to keep the signalization overhead for switching betweendifferent inter-component prediction weights a at sub-picturegranularity at lower bit consumption as the sub-picture signalling maymerely discriminate between a smaller number of possible values for α.

As described above, it is feasible that the syntax element structure 510allows the decoder to derive first and second interval bounds 524therefrom. The corresponding syntax elements in structure 510 may becoded independent/separately from each other, or relative to each other,i.e. differentially. The interval bound values 524 identify elements outof sequence 520, namely using the above-presented exponential functionwhich may be implemented using respective bit shifts. By this measure,the interval bounds 524 indicate to the decoder the co-domain of mapping522.

As also described above, the case of a being zero may be signaled to thedecoder separately using a respective zero flag 526. If the zero flaghas a first state, the decoder sets a to be zero and skips reading anyfirst-weight syntax element 514 for the respective block 440. If thezero flag has the other state, then the decoder reads the first-weightsyntax element 514 from data stream 104 and determines the actual valueof the weight using mapping 522.

Further, as outlined above merely an absolute part 528 of thefirst-weight syntax element 514 may be coded using the truncated unarybinarization, and a sign part of the first-weight syntax element 514 maybe coded previously. In this way, it is feasible for encoder and decoderto appropriately set their lengths, i.e. the number of bin strings, ofbinarization 518 for the absolute path 528 as the sign part 530determines whether the value a of block 440 belongs to those members ofthe co-domain 532 of mapping 522 out of set 520 which have the positivea values, or to the other part thereof consisting of the negative avalues. Naturally, the sign part 530 of the first-weight syntax element514 may not be present and may not be read by a decoder in case thedecoder derives from the high-level syntax element structure 510 thatthe co-domain 530 merely comprises positive a values or merely negativea values, exclusively.

As also became clear from the above discussion, the interval bounds 524and the order in which same are coded in the high-level syntax elementstructure 510 may determine the order in which the absolute part 528“traverses” the members of co-domain 532.

With respect to FIG. 10, a further concrete embodiment summarizingcertain aspects already described above, is illustrated. According tothe embodiment of FIG. 10, encoder and decoder subdivide the picture102/202 commonly with respect to all three components as far as thehybrid prediction within predictors 122/222 is concerned. In FIG. 10,the components are denoted by “1”, “2” and “3”, respectively, andwritten below the respectively illustrated picture. Thesubdivision/partitioning of picture 102/202 into prediction blocks 308may be signaled within the data stream 104 via prediction relatedsubdivision information 600.

Per prediction block 308, prediction parameters may be signaled withinthe data stream 104. These prediction parameters are used for hybridencoding/decoding each component of the picture 102/202. The predictionparameter 602 may be signaled within the data stream 104 for eachcomponent individually, for all components commonly or partiallycomponent specifically and component-globally. For example, theprediction parameter 602 may, for example, distinguish between, interalia, spatially and/or temporally predicted blocks 308 and while, forexample, this indication may be common among the components, thetemporal prediction-related parameters among prediction parameter 602may be signaled within the data stream 104 component-specifically. Usingthe implementation of FIGS. 1 and 2, for example, predictors 122/222 usethe prediction parameter 602 in order to derive, for each component, theprediction signal 120/220.

Further, the data stream 104 signals, in accordance with the embodimentof FIG. 10, a subdivision/partitioning of picture 102/202 into residualor transform blocks, here denoted by reference sign 604. Theresidual/transform-related subdivision information within the datastream 104 is indicated using reference sign 606. As described abovewith respect to FIG. 3, the subdivision/partitioning of picture 102/202into prediction blocks 308 on the one hand and residual/transform blocks604 on the other hand, may at least partially be coupled to each otherin that at least partially the partitioning into residual/transformblocks 604 forms an extension of the hierarchical multi-treesubdivisioning of picture 102/202 into prediction blocks 308 or somehierarchical intermediary subdivision into, for example, coding blocks.

Per residual/transform block, the data stream 104 may comprise residualdata 608 ₁, 608 ₂, 608 ₃ in the form of, for example, quantizedtransform coefficients. Dequantizing and inverse transforming theresidual data 608 ₁ to 608 ₃ reveals a residual signal in the spatialdomain for each component, namely 610 ₁, 610 ₂ and 610 ₃.

As illustrated in FIG. 10, the data stream 104 further comprises aninter-component prediction flag 612 which, in the present example,signals for picture 102/202 globally as to whether or notinter-component prediction is applied/used. If the inter-componentprediction flag 612 signals that inter-component prediction is not used,the residual signals 610 ₁ to 610 ₃ are not combined with each other,but are separately, with respect to each component, used so as tocorrect the prediction signal 120/220. If, however, the inter-componentprediction flag 612 signals the usage of inter-component prediction, thedata stream 104 comprises, per residual/transform block, for eachdependent component 2 and 3, a flag 614 ₂, 614 ₃ signalling whether ornot for the respective component 2/3 inter-component prediction isapplied. If signaled to be applied, the data stream 104 comprises forthe respective residual/transform block for the respective componenti=2/3 an inter-component prediction parameter 616 ₂ and 616 ₃,respectively, corresponding to, for example, a of the above outlineddescription.

Thus, if for example the flag 614 ₂ indicates for the second componentthat inter-component prediction is to be used, the inter-componentprediction parameter 616 ₂ indicates the weight at which the residualsignal 610 ₁ is to be added to the residual signal 610 ₂ so as toreplace residual signal 610 ₂ by the new residual signal 610 ₂′. Thelatter is then used instead of residual signal 610 ₂ so as to correctthe respective prediction signal 120 ₂/220 ₂.

Likewise, if flag 614 ₃ indicates the usage of inter-componentprediction for a respective residual/transform block, then theinter-component prediction parameter 616 ₃ indicates the weight α₃ atwhich the residual signal 610 ₁ is added to the residual signal 610 ₃ soas to replace the latter and result in the new residual signal 610 ₃′,which is then used in order to correct the prediction signal 120 ₃/220 ₃of the third component.

Instead of separately transmitting a first flag 614 _(1/2) conditionallyfollowed by an inter-component prediction parameter 616 _(2/3), anothersignalling may also be feasible. For example, as the weight α_(2/3) maybe a signed value, the domain of possible values of which issymmetrically arranged around zero, the absolute value of α_(2/3) may beused so as to distinguish between the case of not using inter-componentprediction as far as component 2/3 is concerned, and usinginter-component prediction for the respective component 2/3. Inparticular, if the absolute value is zero, this corresponds to not usinginter-component prediction. The signalling of any sign flag for therespective parameter α_(2/3) may then be suppressed in the data stream104. As a reminder, in accordance with the embodiment of FIG. 10, theinter-component prediction is varied on a per residual/transform blockbasis as far as components 2/3 are concerned, the variation includingnot using inter-component prediction at all, α_(2/3)=0, and usinginter-component prediction with varying α_(2/3) (α_(2/3)≠0).

According to a specific syntax example, the inter-component predictionflag 612 may be signaled within a picture parameter set of the datastream 104. The syntax element may be denoted as

cross_component_prediction_enabled_flag

It is noted, however, that the scope of flag 612 may be chosendifferently. For example, flag 612 may relate to smaller units, such asslices of picture 102/202 or greater units such as groups of pictures ora sequence of pictures.

Per residual/transform block, syntax elements 614 ₂, 616 ₂, 614 ₃ and616 ₃ may be signaled conditionally as just described using thefollowing syntax with parameter c indicating the component and,accordingly, assuming one value for component 2 and the other value forcomponent 3, and parameters x0 and y0 denoting, for example, therespective residual/transform block by way of, for example the positionof its upper left corner sample.

  cross_comp_pred( x0, y0, c ) {  log2_res_scale_abs_plus1[ c ]  if(log2_res_scale_abs_plus1[ c ] != 0 )   res_scale_sign_flag[ c ] }

That is, the above syntax would occur in the data stream 104, forexample, for each residual or transform block of the picture twice, onefor each of the second and third components, such as the chromacomponents whereas the luma component would form the base (first)component.

As previously indicated with respect to FIG. 10, the just outlinedsyntax example corresponds to the alternative to the configuration ofFIG. 10: log 2_res_scale_abs_plus1 signals the absolute value of a andif the syntax element is zero, this corresponds to the inter-componentprediction not being used for the respective component c. If used,however, res_scale_sign_flag is signaled and indicates the sign of α.

The semantics of the syntax elements presented so far could be providedas follows:

cross_component_prediction_enabled_flag equal to 1 specifies that log2_res_scale_abs_plus1 and res_scale_sign_flag may be present in thetransform unit syntax for pictures referring to the PPS.cross_component_prediction_enabled_flag equal to 0 specifies that log2_res_scale_abs_plus1 and res_scale_sign_flag are not present forpictures referring to the PPS. When not present, the value ofcross_component_prediction_enabled_flag is inferred to be equal to 0.When ChromaArrayType is not equal to 3, it is a requirement of bitstreamconformance that the value of cross_component_prediction_enabled_flagshall be equal to 0.

log 2_res_scale_abs_plus1 [c] minus 1 specifies the base 2 logarithm ofthe magnitude of the scaling factor ResScaleVal used in cross-componentresidual prediction. When not present, log 2_res_scale_abs_plus1 isinferred equal to 0.

res_scale_sign_flag[c] specifies the sign of the scaling factor used incross-component residual prediction as follows:

-   -   If res_scale_sign_flag[c] is equal to 0, the corresponding        ResScaleVal has a positive value.    -   Otherwise (res_scale_sign_flag[c] is equal to 1), the        corresponding ResScaleVal has a negative value.

The variable ResScaleVal[cldx][x0][y0] specifies the scaling factor usedin cross-component residual prediction. The array indices x0, y0 specifythe location (x0, y0) of the top-left luma sample of the consideredtransform block relative to the top-left luma sample of the picture. Thearray index cldx specifies an indicator for the color component; it isequal to 1 for Cb, and equal to 2 for Cr.

The variable ResScaleVal[cldx][x0][y0] is derived as follows:

-   -   If log 2_res_scale_abs_plus1 [cldx−1] is equal to 0, the        following applies: ResScaleVal[cldx][x0][y0]=0    -   Otherwise (log 2_res_scale_abs_plus1 [cldx−1] is not equal to        0), the following applies: ResScaleVal[cldx][x0][y0]=(1−(log        2_res_scale_abs_plus1        [cldx−1]−1))*(1−2*res_scale_sign_flag[cldx−1])

In the above, ResScaleVal corresponds to the aforementioned α.

That is, the sample values within a residual/transform block 604, forwhich inter-component prediction is used, i.e. for which log2_res_scale_abs_plus1≠0, at positions x, y, i.e. r[x][y], are computedon the basis of the co-located residual sample values ry[x][y] of thefirst component according to, for example,

r[x][y]+=(ResScaleVal[cldx][xTbY][yTbY]*((r _(Y)[x][y]<<BitDepth_(C))>>BitDepth_(Y)))>>3

wherein BitDepth_(C) is the bit depth of the dependent components 2/3and BitDepth_(Y) is the bit depth of the first component.

The right shift “>>3” corresponds to a division by eight. According tothe present example, the signalizable α values are, as alreadyexemplified above, {0, ±0.125, ±0.25, ±0.5, ±1}.

log 2_res_scale_abs_plus1 may be signaled in the data stream using atruncated unary binarization and binary arithmetic coding and binaryarithmetic decoding and truncated unary debinarization, respectively.The binary arithmetic de/coding may be context-adaptively. The contextmay be selected based on the local neighbourhood. For example, per binof the binarization of log 2_res_scale_abs_plus1 a different context maybe chosen. Different sets of contexts may be used for both chromacomponents. Likewise, res_scale_sign_flag may be signaled in the datastream binary arithmetic coding and binary arithmetic decoding,respectively. The binary arithmetic de/coding may be context-adaptively.And different context may be used for both chroma components.Alternatively, the same contexts would be used for both chromacomponents.

As described, the mapping from log 2_res_scale_abs_plus1 to the absolutevalue of α, i.e. ResScaleVal>>3, may be done arithmetically using a bitshift operation, i.e. by an exponential function.

The signalling of log 2_res_scale_abs_plus1 and res_scale_sign_flag forthe two chroma components may be skipped for a certainresidual/transform block if the luma component within the latter iszero. As log 2_res_scale_abs_plus1 and res_scale_sign_flag are examplesfor signalling 614 and 616 in FIG. 10, this means that the decoder maypossibly check whether, for a currently decoded portion of the secondcomponent 208, the spatially corresponding portion 442 of thereconstructed first component signal 256 ₁ is zero and, depending on thecheck, either explicitly read the sub-picture level syntax elements 614₂, 616 ₂, 614 ₃, 616 ₃ from the data stream and perform thereconstruction of the component signals 256′23 from the spatiallycorresponding portion 442, or skip the explicit reading and, optionally,not performing the reconstruction of the second component signal 256′23from the spatially corresponding portion 442, but leaving the secondcomponent signal 256 _(2,3) as it is, instead.

Thus, FIG. 10 exemplifies a decoder configured to decode amulti-component picture 202 spatially sampling a scene with respect todifferent components 206, 208, 210, by reconstructing a first componentsignal 610 ₁ relating to a first component 206 from the data stream 104;and reconstructing a portion 440 of the second component signal 610′23relating to a second (third) component 208/210 of the multi-componentpicture 202 from a spatially corresponding portion 442 of thereconstructed first component signal 610 ₁ and a correction signal 610_(2,3) derived from the data stream. The first component signal 610 ₁ isa prediction residual of a temporally, spatially or inter-viewprediction of the first component 206 of the multi-component picture202, and the decoder may perform the temporal, spatial or inter-viewprediction of the first component 206 of the multi-component picture 202and reconstruct the first component 206 of the multi-component pictureby correcting the temporal, spatial or inter-view prediction of thefirst component using the reconstructed first component signal 610 ₁.The decoder is configured to, at the sub-picture granularity, adaptivelyset, depending on signalling in the data stream, the first weightα_(2,3). To this end, the decoder is configured to, at the sub-picturegranularity, read a first weight's absolute value from the data streamand, in a manner conditionally depending on whether same is zero, afirst weight's sign. The decoder is configured to, at the sub-picturegranularity, skip reading the first weight's absolute value from thedata stream and, in a manner conditionally depending on whether same iszero, the first weight's sign at portions where the first componentsignal is zero. In reconstructing the second component signal, thedecoder adds the spatially corresponding portion of the reconstructedfirst component signal, weighted by the first weight (α₂), to thecorrection signal. The addition may be done in the spatial domain in asample-wise manner. Alternatively, its done in the spectral domain. Theencoder performs the same in the prediction loop.

Although some aspects have been described in the context of anapparatus, it is clear that these aspects also represent a descriptionof the corresponding method, where a block or device corresponds to amethod step or a feature of a method step. Analogously, aspectsdescribed in the context of a method step also represent a descriptionof a corresponding block or item or feature of a correspondingapparatus. Some or all of the method steps may be executed by (or using)a hardware apparatus, like for example, a microprocessor, a programmablecomputer or an electronic circuit. In some embodiments, some one or moreof the most important method steps may be executed by such an apparatus.

Depending on certain implementation requirements, embodiments of theinvention can be implemented in hardware or in software. Theimplementation can be performed using a digital storage medium, forexample a floppy disk, a DVD, a Blu-Ray, a CD, a ROM, a PROM, an EPROM,an EEPROM or a FLASH memory, having electronically readable controlsignals stored thereon, which cooperate (or are capable of cooperating)with a programmable computer system such that the respective method isperformed. Therefore, the digital storage medium may be computerreadable.

Some embodiments according to the invention comprise a data carrierhaving electronically readable control signals, which are capable ofcooperating with a programmable computer system, such that one of themethods described herein is performed.

Generally, embodiments of the present invention can be implemented as acomputer program product with a program code, the program code beingoperative for performing one of the methods when the computer programproduct runs on a computer. The program code may for example be storedon a machine readable carrier.

Other embodiments comprise the computer program for performing one ofthe methods described herein, stored on a machine readable carrier.

In other words, an embodiment of the inventive method is, therefore, acomputer program having a program code for performing one of the methodsdescribed herein, when the computer program runs on a computer.

A further embodiment of the inventive methods is, therefore, a datacarrier (or a digital storage medium, or a computer-readable medium)comprising, recorded thereon, the computer program for performing one ofthe methods described herein. The data carrier, the digital storagemedium or the recorded medium are typically tangible and/ornon-transitionary.

A further embodiment of the inventive method is, therefore, a datastream or a sequence of signals representing the computer program forperforming one of the methods described herein. The data stream or thesequence of signals may for example be configured to be transferred viaa data communication connection, for example via the Internet.

A further embodiment comprises a processing means, for example acomputer, or a programmable logic device, configured to or adapted toperform one of the methods described herein.

A further embodiment comprises a computer having installed thereon thecomputer program for performing one of the methods described herein.

A further embodiment according to the invention comprises an apparatusor a system configured to transfer (for example, electronically oroptically) a computer program for performing one of the methodsdescribed herein to a receiver. The receiver may, for example, be acomputer, a mobile device, a memory device or the like. The apparatus orsystem may, for example, comprise a file server for transferring thecomputer program to the receiver.

In some embodiments, a programmable logic device (for example a fieldprogrammable gate array) may be used to perform some or all of thefunctionalities of the methods described herein. In some embodiments, afield programmable gate array may cooperate with a microprocessor inorder to perform one of the methods described herein. Generally, themethods are advantageously performed by any hardware apparatus.

The apparatus described herein may be implemented using a hardwareapparatus, or using a computer, or using a combination of a hardwareapparatus and a computer.

The methods described herein may be performed using a hardwareapparatus, or using a computer, or using a combination of a hardwareapparatus and a computer.

While this invention has been described in terms of several embodiments,there are alterations, permutations, and equivalents which fall withinthe scope of this invention. It should also be noted that there are manyalternative ways of implementing the methods and compositions of thepresent invention. It is therefore intended that the following appendedclaims be interpreted as including all such alterations, permutationsand equivalents as fall within the true spirit and scope of the presentinvention.

Thus, above description, inter alia described the following embodiments:

According to a first embodiment, a decoder is configured to decode amulti-component picture 202 spatially sampling a scene with respect todifferent components 206, 208, 210, by reconstructing a first componentsignal 256 ₁; 270 ₁ relating to a first component 206 of themulti-component picture 202 from a data stream 104; reconstructing 400 aportion 440 of a second component signal 256′₂; 270′₂ relating to asecond component 208 of the multi-component picture 202 from a spatiallycorresponding portion of the reconstructed first component signal 256 ₁;270 ₁ and a correction signal 256 ₂; 270 ₂ derived from the data stream.

According to a second embodiment, the decoder according to the firstembodiment is configured as a block-based hybrid video decoderconfigured to sub-divide the multi-component picture 202 regularly intotree blocks 302, subdivide the tree blocks using recursive multi-treesubdivisioning into code blocks 304 individually and subdivide each codeblock using recursive multi-tree subdivisioning into prediction blocks308 and using recursive multi-tree subdivisioning into residual blocks312 individually, and subdivide the residual blocks into transformblocks 316; select prediction modes depending on the data stream at agranularity depending on the code blocks or depending on the predictionblocks; set prediction parameters depending on the data stream at agranularity of the prediction blocks; derive a prediction signal 220 ₁,220 ₂, 220 ₃ using the prediction modes and prediction parameters;derive a residual signal 256 ₁, 256′₂, 256′₃ within each residual blockby performing inverse transformations within the transform blocksindividually, and reconstruct the multi-component picture 202 bycorrecting the prediction signal using the residual signal, the decoderbeing responsive to a signalling 614 ₂; 614 ₃ in the data stream so asto, at a granularity of the residual blocks and/or transform blocks,switch between performing the reconstructing of the second componentsignal from the spatially corresponding portion of the reconstructedfirst component signal and the correction signal and a reconstructingthe second component signal from the correction signal irrespective thespatially corresponding portion of the reconstructed first componentsignal.

According to a third embodiment, the decoder according to the firstembodiment is configured such that the first component signal is aprediction residual of a temporally, spatially or inter-view predictionof the first component 206 of the multi-component picture 202, and toperform the temporal, spatial or inter-view prediction of the firstcomponent 206 of the multi-component picture 202 and reconstruct thefirst component 206 of the multi-component picture by correcting thetemporal, spatial or inter-view prediction of the first component usingthe reconstructed first component signal.

According to a fourth embodiment, the decoder according to the firstembodiment is configured such that the second component signal is aprediction residual of a temporal, spatial or inter-view prediction ofthe second component 208 of the multi-component picture 202, and toperform the temporal, spatial or inter-view prediction of the secondcomponent 208 of the multi-component picture and reconstruct the secondcomponent 208 of the multi-component picture 202 by correcting thetemporal, spatial or inter-view prediction of the multi-componentpicture 202 using the reconstructed second component signal.

According to a fifth embodiment, the decoder according to the firstembodiment is configured to obtain the correction signal 256 ₂ byperforming an inverse spectral transformation 226 ₂ onto spectralcoefficients relating to the second component 208 derived from the datastream 104 so as to obtain the correction signal in the spatial domain.

According to a sixth embodiment, the decoder according to the firstembodiment is configured to, in reconstructing the second componentsignal, adaptively set a first weight α₂ at which the spatiallycorresponding portion 442 of the reconstructed first component signalinfluences the reconstruction of the second component signal at asub-picture granularity.

According to a seventh embodiment, the decoder according to the sixthembodiment is configured to, at the sub-picture granularity, adaptivelyset, depending on signalling in the data stream, the first weight α₂.

According to an eighth embodiment, the decoder according to the sixthembodiment is configured to, at the sub-picture granularity, read afirst weight's absolute value from the data stream and, in a mannerconditionally depending on whether same is zero, a first weight's sign.

According to a ninth embodiment, the decoder according to the eighthembodiment is configured to, at the sub-picture granularity, skipreading the first weight's absolute value from the data stream and, in amanner conditionally depending on whether same is zero, the firstweight's sign at portions where the first component signal is zero.

According to a tenth embodiment, the decoder according to the sixthembodiment is configured to, in reconstructing the second componentsignal, add the spatially corresponding portion 442 of the reconstructedfirst component signal, weighted by the first weight α₂, to thecorrection signal.

According to an eleventh embodiment, the decoder according to the tenthembodiment is configured to, in reconstructing the second componentsignal, perform the addition in the spatial domain in a sample-wisemanner.

According to a twelfth embodiment, the decoder according to the sixthembodiment is configured to set the first weight by deriving ahigh-level syntax element structure 510 from the data stream, having atleast picture scope; constructing, at the at least picture scope, amapping 522 from a domain set of possible bin strings 518 of apredetermined binarization onto a co-domain 520 of possible values ofthe first weight; and deriving the first weight by reading, atsub-picture granularity, a first-weight syntax element 514 from the datastream using the predetermined binarization and subjecting thefirst-weight syntax element's bin string to the mapping.

According to a thirteenth embodiment, the decoder according to thetwelfth embodiment is configured to derive from the high-level syntaxelement structure lower and upper bounds 524 of an interval of co-domainvalues out of a predetermined set of possible non-zero values of thefirst weight, and, in deriving the first weight, additionally read, atsub-picture granularity, a zero flag 526 from the data stream indicatingwhether the first weight shall be zero or not with performing thereading of the first-weight syntax element and the subjectingconditionally depending on the zero flag.

According to a fourteenth embodiment, the decoder according to thetwelfth embodiment is configured to, in constructing the mapping, derivefrom the high-level syntax element structure sign and absolute value ofa lower bound integer value and sign and absolute value of a upper boundinteger value and apply an integer-domain exponential function onto theabsolute values of lower bound integer value and upper bound integervalue and grab-out, out of a co-domain of the integer-domain exponentialfunction exclusive zero, the co-domain of possible values of the firstweight.

According to a fifteenth embodiment, the decoder according to thetwelfth embodiment is configured to use a truncated unary binarizationas the predetermined binarization for an absolute value part of thefirst-weight syntax element and, in deriving the first weight, read asign part 530 of the first-weight syntax element from the data streambefore the absolute part 530 of the first-weight syntax element and seta length of the truncated unary binarization of the absolute part of thefirst-weight syntax element depending on the sign part and the co-domainof possible values of the first weight.

According to a sixteenth embodiment, the decoder according to thetwelfth embodiment is configured to derive from the high-level syntaxelement structure first and second interval bounds 524 and the decoderis configured to use a truncated unary binarization of TU bin strings asthe predetermined binarization for an absolute value part of thefirst-weight syntax element and, in constructing the mapping, reverse anorder the possible values onto which the TU bin strings are mappedtraverse the co-domain of possible values depending on a comparison ofthe first and second interval bounds.

According to a seventeenth embodiment, the decoder according to thefirst embodiment is configured to, in reconstructing the secondcomponent signal 208, adaptively set a second weight at which thecorrection signal influences the reconstruction of the second componentsignal at a sub-picture granularity.

According to an eighteenth embodiment, the decoder according to thefirst embodiment is configured to, in reconstructing the secondcomponent signal, adaptively set weights of a weighted sum of thecorrection signal and the spatially corresponding portion 442 of thereconstructed first component signal at a sub-picture granularity anduse the weighted sum as a scalar argument of a scalar function which is,at least per picture, constant so as to obtain the reconstructed secondcomponent signal.

According to a nineteenth embodiment, the decoder according to the firstembodiment is configured to, in reconstructing the second componentsignal, adaptively set weights of a weighted sum of the correctionsignal, the spatially corresponding portion 442 of the reconstructedfirst component signal and a constant at a sub-picture granularity anduse the weighted sum as a scalar argument of a scalar function which is,at least per picture, constant so as to obtain the reconstructed secondcomponent signal.

According to a twentieth embodiment, the decoder according to theeighteenth embodiment is configured to set the weights in abackward-driven manner based on a local neighbourhood.

According to a twenty-first embodiment, the decoder according to theeighteenth embodiment is configured to set the weights in abackward-driven manner based on a local neighbourhood, with correctingthe weights in a forward-driven manner.

According to a twenty-second embodiment, the decoder according to thetwentieth embodiment is configured to set the weights in abackward-driven manner based on attributes of an already decoded portionof the multi-component picture.

According to a twenty-third embodiment, the decoder according to theeighteenth embodiment is configured to set the weights, in a combinedbackward and forward adaptive manner, or a forward-adaptive manner, abackward-adaptive manner, to default values, at a first spatialgranularity, and refine the weights in a backward-driven manner based ona local neighbourhood at a second spatial granularity being finer thanthe first spatial granularity.

According to a twenty-fourth embodiment, the decoder according to thesixteenth embodiment is configured to set the weights to one of mdifferent states depending on m-ary sub-picture level syntax elementswherein the decoder is configured to derive m from an higher-levelsyntax element 510.

According to a twenty-fifth embodiment, the decoder according to thefirst embodiment is configured to adaptively switch, at a sub-picturegranularity, in reconstructing the second component signal, betweenperforming an inverse spectral transformation onto spectral coefficientsrelating to the second component 208 derived from the data stream so asto obtain the correction signal x in a spatial domain and reconstructing400 the second component signal z using the correction signal x in thespatial domain, and obtaining the correction signal x in a spectraldomain from the data stream, reconstructing 400, in the spectral domain,the second component signal z using the correction signal x as obtainedin the spectral domain, and subjecting the, in the spectral domain,reconstructed second component signal z to an inverse spectraltransformation.

According to a twenty-sixth embodiment, the decoder according to thetwenty-fifth embodiment is configured to perform the adaptivelyswitching in a backward-adaptive manner and/or forward-adaptive manner490.

According to a twenty-seventh embodiment, the decoder according to thefirst embodiment is configured to adaptively switch, at a sub-picturegranularity, a direction of reconstruction of the second componentsignal between performing the reconstruction of the second componentsignal from the spatially corresponding portion of the reconstructedfirst component signal and reversing the reconstruction so as toreconstruct of the first component signal from a spatially correspondingportion of the reconstructed second component signal.

According to a twenty-eighth embodiment, the decoder according to thefirst embodiment is configured to adaptively switch, responsive to asyntax element 472 signalling an order among the first and secondcomponent signals, a direction of reconstruction of the second componentsignal between performing the reconstruction of the second componentsignal from the spatially corresponding portion of the reconstructedfirst component signal and reversing the reconstruction so as toreconstruct of the first component signal from a spatially correspondingportion of the reconstructed second component signal.

According to a twenty-ninth embodiment, the decoder according to thefirst embodiment is configured to adaptively switch, at a sub-picturegranularity, the reconstruction of the second component signal betweenreconstructing same merely based on the reconstructed first componentsignal and reconstructing same based on the reconstructed firstcomponent signal and a third reconstructed component signal.

According to a thirtieth embodiment, in the decoder according to thefirst embodiment, the first and second components are colour components.

According to a thirty-first embodiment, in the decoder according to thefirst embodiment, the first component is luma and the second componentis a chroma component.

According to a thirty-second embodiment, in the decoder according to thefirst embodiment, the decoder is responsive to a first syntax element612 in the data stream so as to, depending on the first syntax element612, enable the reconstruction of the second component signal based onthe reconstructed first component signal, read sub-picture level syntaxelements 614 ₂, 616 ₂, 614 ₃, 616 ₃ from the data stream in parsing thedata stream and adapt the reconstruction of the second component signalbased on the reconstructed first component signal at a sub-picturegranularity based on the sub-picture level syntax elements, and disablethe reconstruction of the second component signal based on thereconstructed first component signal, and change the parsing the datastream to address the data stream not comprising the sub-picture levelsyntax elements.

According to a thirty-third embodiment, in the decoder according to thefirst embodiment, the decoder is configured to, in a backward-drivenmanner, switch locally between enabling the reconstruction of the secondcomponent signal based on the reconstructed first component signal, anddisabling the reconstruction of the second component signal based on thereconstructed first component signal.

According to a thirty-fourth embodiment, in the decoder according to thethirty-third embodiment, the decoder is configured to perform the localswitching in a backward-driven manner.

According to a thirty-fifth embodiment, in the decoder according to thethirty-third embodiment, the decoder is configured such that the firstcomponent signal is a prediction residual of a temporally, spatially orinter-view prediction of the first component of the multi-componentpicture, and to perform the temporal, spatial or inter-view predictionof the first component of the multi-component picture and reconstructthe first component of the multi-component picture by correcting thetemporal, spatial or inter-view prediction of the first component usingthe reconstructed first component signal, the decoder is configured suchthat the second component signal is a prediction residual of a temporal,spatial or inter-view prediction of the second component of themulti-component picture, and to perform the temporal, spatial orinter-view prediction of the second component of the multi-componentpicture and reconstruct the second component of the multi-componentpicture by correcting the temporal, spatial or inter-view prediction ofthe multi-component picture using the reconstructed second componentsignal, and the decoder is configured to perform the local switching bylocally checking whether the first and the second component signals areprediction residuals of a spatial prediction and whether anintra-prediction mode of the spatial prediction coincides, or by locallychecking whether the first and the second component signals areprediction residuals of a spatial prediction and whether anintra-prediction mode of the spatial prediction does not deviate by morethan a predetermined amount.

According to a thirty-sixth embodiment, in the decoder according to thethirty-third embodiment, the decoder is configured to decide on thelocal switching firstly in a backward-driven manner with modifying thedecision in a forward-adaptive manner responsive to a signalling in thedata stream.

According to a thirty-seventh embodiment, in the decoder according tothe first embodiment, the decoder is responsive to a second syntaxelement in the data stream so as to, depending on the second syntaxelement, read sub-picture level syntax elements from the data stream inparsing the data stream and adapt the reconstruction of the secondcomponent signal based on the reconstructed first component signal at asub-picture granularity based on the sub-picture level syntax elements,and perform the reconstruction of the second component signal based onthe reconstructed first component signal non-adaptively.

According to a thirty-eighth embodiment, in the decoder according to thefirst embodiment, the first and second components 206, 208 are two ofthree colour components, and the decoder is configured to alsoreconstruct a third component signal relating to the third colourcomponent 210 of the multi-component picture 202 from a spatiallycorresponding portion of the reconstructed first or second componentsignal and a correction signal derived from the data stream for thethird component, wherein the decoder is configured to perform thereconstruction of the second and third component signals on asub-picture level adaptively individually.

According to a thirty-ninth embodiment, in the decoder according to thefirst embodiment, the first component 206 is luma, the second component208 is a first chroma component and the third component 210 is a secondchroma component and the decoder is configured to entropy decode firstsub-picture level syntax elements 614 ₂, 616 ₂ for adapting thereconstruction of the second component signal relating to the firstcolour component of the multi-component picture and second sub-picturelevel syntax elements 614 ₃, 616 ₃ for adapting the reconstruction ofthe third component signal relating to the first colour component of themulti-component picture from the spatially corresponding portion of thereconstructed first or second component signal context-adaptively usingthe same contexts.

According to a fortieth embodiment, in the decoder according to thefirst embodiment, the first component is luma, the second component is afirst chroma component and the third component is a second chromacomponent and the decoder is configured to entropy decode firstsub-picture level syntax elements for adapting the reconstruction of thesecond component signal relating to the first colour component of themulti-component picture and second sub-picture level syntax elements foradapting the reconstruction of the third component signal relating tothe first colour component of the multi-component picture from thespatially corresponding portion of the reconstructed first or secondcomponent signal context-adaptively using separate contexts.

According to a forty-first embodiment, in the decoder according to thefirst embodiment, the decoder is configured to read sub-picture levelsyntax elements from the data stream in parsing the data stream andadapt the reconstruction of the second component signal based on thereconstructed first component signal at a sub-picture granularity basedon the sub-picture level syntax elements, and, in parsing the datastream, check as to whether, for a currently decoded portion of thesecond component, the spatially corresponding portion 442 of thereconstructed first component signal is zero and, depending on thecheck, explicitly read the sub-picture level syntax elements from thedata stream and perform the reconstruction of the second componentsignal from the spatially corresponding portion of the reconstructedfirst component signal, or skip the explicit reading.

According to a forty-first embodiment, in the decoder according to thefirst embodiment, the decoder is configured to entropy decode thesub-picture level syntax elements from the data stream using a GolombRice Code.

According to a forty-first embodiment, in the decoder according to theforty-second embodiment, the decoder is configured to, in entropydecoding the sub-picture level syntax elements from the data stream,binary arithmetic decode bins of the Golomb Rice Code.

According to a forty-first embodiment, in the decoder according to theforty-third embodiment, the decoder is configured to, in entropydecoding the sub-picture level syntax elements from the data stream,binary arithmetic decode bins of the Golomb Rice Code at different binpositions using different contexts.

According to a forty-first embodiment, in the decoder according to theforty-third embodiment, the decoder is configured to, in entropydecoding the sub-picture level syntax elements from the data stream,binary arithmetic decode bins of the Golomb Rice Code at bin positionsexceeding a predetermined value, context-less.

According to a forty-first embodiment, in the decoder according to thefirst embodiment, the decoder is configured to, in reconstructing thesecond component signal, spatially re-scale, and/or perform a bit-depthprecision mapping on, the spatially corresponding portion of thereconstructed first component signal.

According to a forty-first embodiment, in the decoder according to theforty-sixth embodiment, the decoder is configured to adapt the spatiallyre-scaling, and/or performance of the bit-depth precision mapping, in abackward- and/or forward-adaptive manner.

According to a forty-first embodiment, in the decoder according to theforty-sixth embodiment, the decoder is configured to adapt the spatiallyre-scaling by selecting a spatial filter, in a backward- and/orforward-adaptive manner.

According to a forty-first embodiment, in the decoder according to theforty-eighth embodiment, the decoder is configured to adapt theperformance of the bit-depth precision mapping, by selecting a mappingfunction, in a backward- and/or forward-adaptive manner.

According to a fiftieth embodiment, in the decoder according to thefirst embodiment, the decoder is configured to, in reconstructing thesecond component signal, reconstruct the second component signal from aspatially low-pass filtered version of the reconstructed first componentsignal.

According to a fifty-first embodiment, in the decoder according to thefiftieth embodiment, the decoder is configured to perform thereconstruction of the second component signal from the spatiallylow-pass filtered version of the reconstructed first component signal ina forward adaptive manner or in a backward-adaptive manner.

According to a fifty-second embodiment, in the decoder according to thefiftieth embodiment, the decoder is configured to adapt thereconstruction of the second component signal from the spatiallylow-pass filtered version of the reconstructed first component signal bysetting a low-pass filter used for the low-pass filtering in a forwardadaptive manner or in a backward-adaptive manner.

According to a fifty-third embodiment, in the decoder according to theforty-fifth embodiment, the decoder is configured to perform the spatiallow-pass filtering leading to the low-pass filtered version of thereconstructed first component signal using binning.

According to a fifty-fourth embodiment, an encoder is configured toencode a multi-component picture 202 spatially sampling a scene withrespect to different components 206, 208, 210, by encoding 400 a portion440 of a second component signal 256′₂; 270′₂ relating to a secondcomponent 208 of the multi-component picture 202 by inter-componentprediction on the basis of a spatially corresponding portion of areconstructed first component signal 256 ₁; 270 ₁ and inserting acorrection signal 256 ₂; 270 ₂ for correcting the inter-componentprediction into the data stream.

According to a fifty-fifth embodiment, a method for decoding amulti-component picture 202 spatially sampling a scene with respect todifferent components 206, 208, 210 comprises reconstructing a firstcomponent signal 256 ₁; 270 ₁ relating to a first component 206 of themulti-component picture 202 from a data stream 104; and reconstructing400 a portion 440 of a second component signal 256′₂; 270′₂ relating toa second component 208 of the multi-component picture 202 from aspatially corresponding portion of the reconstructed first componentsignal 256 ₁; 270 ₁ and a correction signal 256 ₂; 270 ₂ derived fromthe data stream.

According to a fifty-sixth embodiment, a method for encoding amulti-component picture 202 spatially sampling a scene with respect todifferent components 206, 208, 210 comprises encoding 400 a portion 440of a second component signal 256′₂; 270′₂ relating to a second component208 of the multi-component picture 202 by inter-component prediction onthe basis of a spatially corresponding portion of a reconstructed firstcomponent signal 256 ₁; 270 ₁ and inserting a correction signal 256 ₂;270 ₂ for correcting the inter-component prediction into the datastream.

According to a fifty-seventh embodiment, a computer program has aprogram code for performing, when running on a computer, a methodaccording to the fifty-fifth or fifty-sixth embodiment.

1. A decoder configured to decode a multi-component picture spatiallysampling a scene with respect to different components, by reconstructinga first component signal relating to a first component of themulti-component picture from a data stream; reconstructing a portion ofa second component signal relating to a second component of themulti-component picture from a spatially corresponding portion of thereconstructed first component signal and a correction signal derivedfrom the data stream, wherein the first and second components are colourcomponents and the first component signal is a prediction residual of atemporally, spatially or inter-view prediction of the first component ofthe multi-component picture and the second component signal is aprediction residual of a temporal, spatial or inter-view prediction ofthe second component of the multi-component picture.
 2. The decoderaccording to claim 1, wherein the decoder is configured as a block-basedhybrid video decoder configured to sub-divide the multi-componentpicture regularly into tree blocks, subdivide the tree blocks usingrecursive multi-tree subdivisioning into code blocks individually andsubdivide each code block using recursive multi-tree subdivisioning intoprediction blocks and using recursive multi-tree subdivisioning intoresidual blocks individually, and subdivide the residual blocks intotransform blocks; select prediction modes depending on the data streamat a granularity depending on the code blocks or depending on theprediction blocks; set prediction parameters depending on the datastream at a granularity of the prediction blocks; derive a predictionsignal using the prediction modes and prediction parameters; derive aresidual signal within each residual block by performing inversetransformations within the transform blocks individually, andreconstruct the multi-component picture by correcting the predictionsignal using the residual signal, wherein the decoder is responsive to asignalling in the data stream so as to, at a granularity of the residualblocks and/or transform blocks, switch between performing thereconstructing of the second component signal from the spatiallycorresponding portion of the reconstructed first component signal andthe correction signal and a reconstructing the second component signalfrom the correction signal irrespective the spatially correspondingportion of the reconstructed first component signal.
 3. The decoderaccording to claim 1, wherein the decoder is configured to acquire thecorrection signal by performing an inverse spectral transformation ontospectral coefficients relating to the second component derived from thedata stream so as to acquire the correction signal in the spatialdomain.
 4. The decoder according to claim 1, wherein the decoder isconfigured to, in reconstructing the second component signal, adaptivelyset a first weight at which the spatially corresponding portion of thereconstructed first component signal influences the reconstruction ofthe second component signal at a sub-picture granularity.
 5. The decoderaccording to claim 4, wherein the decoder is configured to, at thesub-picture granularity, adaptively set, depending on signalling in thedata stream, the first weight.
 6. The decoder according to claim 4,wherein the decoder is configured to set the first weight by deriving ahigh-level syntax element structure from the data stream, comprising atleast picture scope; constructing, at the at least picture scope, amapping from a domain set of possible bin strings of a predeterminedbinarization onto a co-domain of possible values of the first weightusing the high-level syntax element structure; and deriving the firstweight by reading, at sub-picture granularity, a first-weight syntaxelement from the data stream using the predetermined binarization andsubjecting the first-weight syntax element's bin string to the mapping.7. The decoder according to claim 1, wherein the decoder is configuredto, in reconstructing the second component signal, adaptively set asecond weight at which the correction signal influences thereconstruction of the second component signal at a sub-picturegranularity.
 8. The decoder according to claim 1, wherein the decoder isconfigured to, in reconstructing the second component signal, adaptivelyset weights of a weighted sum of the correction signal and the spatiallycorresponding portion of the reconstructed first component signal at asub-picture granularity and use the weighted sum as a scalar argument ofa scalar function which is, at least per picture, constant so as toacquire the reconstructed second component signal.
 9. The decoderaccording to claim 1, wherein the decoder is configured to adaptivelyswitch, at a sub-picture granularity, in reconstructing the secondcomponent signal, between performing an inverse spectral transformationonto spectral coefficients relating to the second component derived fromthe data stream so as to acquire the correction signal in a spatialdomain and reconstructing the second component signal using thecorrection signal in the spatial domain, and acquiring the correctionsignal in a spectral domain from the data stream, reconstructing, in thespectral domain, the second component signal using the correction signalas acquired in the spectral domain, and subjecting the, in the spectraldomain, reconstructed second component signal to an inverse spectraltransformation.
 10. The decoder according to claim 1, wherein thedecoder is configured to adaptively switch, at a sub-picturegranularity, a direction of reconstruction of the second componentsignal between performing the reconstruction of the second componentsignal from the spatially corresponding portion of the reconstructedfirst component signal and reversing the reconstruction so as toreconstruct of the first component signal from a spatially correspondingportion of the reconstructed second component signal.
 11. The decoderaccording to claim 1, wherein the decoder is configured to, in abackward-driven manner, switch locally between enabling thereconstruction of the second component signal based on the reconstructedfirst component signal, and disabling the reconstruction of the secondcomponent signal based on the reconstructed first component signal. 12.The decoder according to claim 11, wherein the decoder is configuredsuch that the first component signal is a prediction residual of atemporally, spatially or inter-view prediction of the first component ofthe multi-component picture, and to perform the temporal, spatial orinter-view prediction of the first component of the multi-componentpicture and reconstruct the first component of the multi-componentpicture by correcting the temporal, spatial or inter-view prediction ofthe first component using the reconstructed first component signal, thedecoder is configured such that the second component signal is aprediction residual of a temporal, spatial or inter-view prediction ofthe second component of the multi-component picture, and to perform thetemporal, spatial or inter-view prediction of the second component ofthe multi-component picture and reconstruct the second component of themulti-component picture by correcting the temporal, spatial orinter-view prediction of the multi-component picture using thereconstructed second component signal, and the decoder is configured toperform the local switching by locally checking whether the first andthe second component signals are prediction residuals of a spatialprediction and whether an intra-prediction mode of the spatialprediction coincides, or by locally checking whether the first and thesecond component signals are prediction residuals of a spatialprediction and whether an intra-prediction mode of the spatialprediction does not deviate by more than a predetermined amount.
 13. Thedecoder according to claim 1, wherein the decoder is responsive to asecond syntax element in the data stream so as to, depending on thesecond syntax element, read sub-picture level syntax elements from thedata stream in parsing the data stream and adapt the reconstruction ofthe second component signal based on the reconstructed first componentsignal at a sub-picture granularity based on the sub-picture levelsyntax elements, and perform the reconstruction of the second componentsignal based on the reconstructed first component signal non-adaptively.14. The decoder according to claim 1, wherein the first and secondcomponents are two of three colour components, and the decoder isconfigured to also reconstruct a third component signal relating to thethird colour component of the multi-component picture from a spatiallycorresponding portion of the reconstructed first or second componentsignal and a correction signal derived from the data stream for thethird component, wherein the decoder is configured to perform thereconstruction of the second and third component signals on asub-picture level adaptively individually.
 15. The decoder according toclaim 1, wherein the decoder is configured to read sub-picture levelsyntax elements from the data stream in parsing the data stream andadapt the reconstruction of the second component signal based on thereconstructed first component signal at a sub-picture granularity basedon the sub-picture level syntax elements, and, in parsing the datastream, check as to whether, for a currently decoded portion of thesecond component, the spatially corresponding portion of thereconstructed first component signal is zero and, depending on thecheck, explicitly read the sub-picture level syntax elements from thedata stream and perform the reconstruction of the second componentsignal from the spatially corresponding portion of the reconstructedfirst component signal, or skip the explicit reading.
 16. The decoderaccording to claim 1, wherein the decoder is configured to, inreconstructing the second component signal, spatially re-scale, and/orperform a bit-depth precision mapping on, the spatially correspondingportion of the reconstructed first component signal.
 17. The decoderaccording to claim 1, wherein the decoder is configured to, inreconstructing the second component signal, reconstruct the secondcomponent signal from a spatially low-pass filtered version of thereconstructed first component signal.
 18. An encoder configured toencode a multi-component picture spatially sampling a scene with respectto different components, by encoding a portion of a second componentsignal relating to a second component of the multi-component picture byprediction from a spatially corresponding portion of a reconstructedfirst component signal and inserting a correction signal for correctingthe prediction into the data stream.
 19. A method for decoding amulti-component picture spatially sampling a scene with respect todifferent components, comprising reconstructing a first component signalrelating to a first component of the multi-component picture from a datastream; and reconstructing a portion of a second component signalrelating to a second component of the multi-component picture from aspatially corresponding portion of the reconstructed first componentsignal and a correction signal derived from the data stream, wherein thefirst and second components are colour components and the firstcomponent signal is a prediction residual of a temporally, spatially orinter-view prediction of the first component of the multi-componentpicture and the second component signal is a prediction residual of atemporal, spatial or inter-view prediction of the second component ofthe multi-component picture.
 20. A method for encoding a multi-componentpicture spatially sampling a scene with respect to different components,comprising encoding a portion of a second component signal relating to asecond component of the multi-component picture by inter-componentprediction on the basis of a spatially corresponding portion of areconstructed first component signal and inserting a correction signalfor correcting the inter-component prediction into the data stream,wherein the first and second components are colour components and thefirst component signal is a prediction residual of a temporally,spatially or inter-view prediction of the first component of themulti-component picture and the second component signal is a predictionresidual of a temporal, spatial or inter-view prediction of the secondcomponent of the multi-component picture.